## One world numeration seminar

#### Jour, heure et lieu

Le mardi à 14h30, online

Le calendrier des séances (format iCal).

Pour ajouter le calendrier des séances à votre agenda favori, souscrire au calendrier en indiquant ce lien.

#### Contact(s)

This is an international online seminar on numeration systems and related topics. If you want to participate, please write to numeration@irif.fr. For more information, in particular slides and videos of past talks, visit Numeration - OWNS homepage.

### Prochaines séances

One world numeration seminar

Mardi 17 septembre 2024, 14 heures, Online

**Simon Kristensen** (Aarhus Universitet) *On the distribution of sequences of the form $(q_n y)$*

One world numeration seminar

Mardi 1 octobre 2024, 14 heures, Online

**Dong Han Kim** (Dongguk University) *Uniform Diophantine approximation on the Hecke group $H_4$*

One world numeration seminar

Mardi 12 novembre 2024, 14 heures, Online

**Florian Luca** (Stellenbosch University) *Non encore annoncé.*

One world numeration seminar

Mardi 26 novembre 2024, 14 heures, Online

**Hoajie Ren** (Technion) *Non encore annoncé.*

One world numeration seminar

Mardi 10 décembre 2024, 14 heures, Online

**Meng Wu** (Oulun yliopisto) *Non encore annoncé.*

### Séances passées

#### Année 2024

One world numeration seminar

Mardi 18 juin 2024, 14 heures, Online

**Noy Soffer Aranov** (Technion) *Escape of Mass of the Thue Morse Sequence*

One world numeration seminar

Mardi 21 mai 2024, 14 heures, Online

**Gaétan Guillot** (Université Paris-Saclay) *Approximation of linear subspaces by rational linear subspaces*

One world numeration seminar

Mardi 7 mai 2024, 14 heures, Online

**Tom Kempton** (University of Manchester) *The Dynamics of the Fibonacci Partition Function*

One world numeration seminar

Mardi 23 avril 2024, 14 heures, Online

**Shunsuke Usuki** (Kyoto University) *On a lower bound of the number of integers in Littlewood's conjecture*

One world numeration seminar

Mardi 26 mars 2024, 14 heures, Online

**Nikita Shulga** (La Trobe University) *Radical bound for Zaremba’s conjecture*

One world numeration seminar

Mardi 12 mars 2024, 14 heures, Online

**Joël Ouaknine** (Max Planck Institute for Software Systems) *The Skolem Landscape*

One world numeration seminar

Mardi 30 janvier 2024, 14 heures, Online

**Cathy Swaenepoel** (IMJ-PRG) *Reversible primes*

This is a joint work with Cécile Dartyge, Bruno Martin, Joël Rivat and Igor Shparlinski.

One world numeration seminar

Mardi 16 janvier 2024, 14 heures, Online

**Karma Dajani** (Universiteit Utrecht) *Alternating N-continued fraction expansions*

#### Année 2023

One world numeration seminar

Mardi 12 décembre 2023, 14 heures, Online

**Yasushi Nagai** (Shinshu University) *Overlap algorithm for general S-adic tilings*

One world numeration seminar

Mardi 28 novembre 2023, 14 heures, Online

**Claudio Bonanno** (Università di Pisa) *Asymptotic behaviour of the sums of the digits for continued fraction algorithms*

One world numeration seminar

Mardi 14 novembre 2023, 14 heures, Online

**Jana Lepšová** (České vysoké učení technické v Praze, Université de Bordeaux) *Dumont-Thomas numeration systems for ℤ*

One world numeration seminar

Mardi 31 octobre 2023, 14 heures, Online

**Stefano Marmi** (Scuola Normale Superiore) *Complexified continued fractions and complex Brjuno and Wilton functions*

One world numeration seminar

Mardi 17 octobre 2023, 14 heures, Online

**Fumichika Takamizo** (Osaka Metropolitan University) *Finite $\beta$-expansion of natural numbers*

One world numeration seminar

Mardi 3 octobre 2023, 14 heures, Online

**Manfred Madritsch** (Université de Lorraine) *Construction of absolutely normal numbers*

In the present talk we want to generalize this notion to normality in measure preserving systems like $\beta$-expansions and continued fraction expansions. Then we show constructions of numbers that are (absolutely) normal with respect to several different expansions.

One world numeration seminar

Mardi 19 septembre 2023, 14 heures, Online

**James Worrell** (University of Oxford) *Transcendence of Sturmian Numbers over an Algebraic Base*

We give an application of our main result to the theory of dynamical systems. We show that for a Cantor set C arising as the set of limit points of a contracted rotation f on the unit interval, where f is assumed to have an algebraic slope, all elements of C except its endpoints 0 and 1 are transcendental.

This is joint work with Florian Luca and Joel Ouaknine.

One world numeration seminar

Mardi 5 septembre 2023, 14 heures, Online

**Mark Pollicott** (University of Warwick) *Complex Dimensions and Fractal Strings*

One world numeration seminar

Mardi 9 mai 2023, 14 heures, Online

**Craig S. Kaplan** (University of Waterloo) *An aperiodic monotile*

One world numeration seminar

Mardi 25 avril 2023, 15 heures, Online

**Ronnie Pavlov** (University of Denver) *Subshifts of very low complexity*

One world numeration seminar

Mardi 18 avril 2023, 14 heures, Online

**Anton Lukyanenko** (George Mason University) *Serendipitous decompositions of higher-dimensional continued fractions*

This is joint work with Joseph Vandehey.

One world numeration seminar

Mardi 28 mars 2023, 14 heures, Online

**Roland Zweimüller** (Universität Wien) *Variations on a theme of Doeblin*

(Part of this is joint work with Max Auer.)

One world numeration seminar

Mardi 21 mars 2023, 14 heures, Online

**Demi Allen** (University of Exeter) *Diophantine Approximation for systems of linear forms - some comments on inhomogeneity, monotonicity, and primitivity*

One world numeration seminar

Mardi 7 mars 2023, 14 heures, Online

**Derong Kong** (Chongqing University) *Critical values for the beta-transformation with a hole at 0*

One world numeration seminar

Mardi 14 février 2023, 14 heures, Online

**Yining Hu** (Huazhong University of Science and Technology) *Algebraic automatic continued fractions in characteristic 2*

One world numeration seminar

Mardi 7 février 2023, 14 heures, Online

**Ale Jan Homburg** (Universiteit van Amsterdam, Vrije Universiteit Amsterdam) *Iterated function systems of linear expanding and contracting maps on the unit interval*

This dynamics depends on the Lyapunov exponent.

For a negative Lyapunov exponent we establish synchronization, meaning convergence of orbits with different initial points. For a vanishing Lyapunov exponent we establish intermittency, where orbits are close for a set of iterates of full density, but are intermittently apart. For a positive Lyapunov exponent we show the existence of an absolutely continuous stationary measure for the two-point dynamics and discuss its consequences.

For nonnegative Lyapunov exponent and pairs $(M,N)$ that are multiplicatively dependent integers, we provide explicit expressions for absolutely continuous stationary measures of the two-point dynamics. These stationary measures are infinite $\sigma$-finite measures in the case of zero Lyapunov exponent.

This is joint work with Charlene Kalle.

One world numeration seminar

Mardi 31 janvier 2023, 14 heures, Online

**Slade Sanderson** (Universiteit Utrecht) *Matching for parameterised symmetric golden maps*

Joint with Karma Dajani.

One world numeration seminar

Mardi 24 janvier 2023, 14 heures, Online

**Kiko Kawamura** (University of North Texas) *The partial derivative of Okamoto's functions with respect to the parameter*

In this talk, we consider the partial derivative of Okomoto's functions with respect to the parameter a. We place a significant focus on a = 1/3 to describe the properties of a nowhere differentiable function K(x) for which the set of points of infinite derivative produces an example of a measure zero set with Hausdorff dimension 1.

This is a joint work with T. Mathis and M.Paizanis (undergraduate students) and N.Dalaklis (graduate student). The talk is very accessible and includes many computer graphics.

One world numeration seminar

Mardi 10 janvier 2023, 14 heures, Online

**Roswitha Hofer** (JKU Linz) *Exact order of discrepancy of normal numbers*

So far the best upper bounds for $D_N$ for explicitly known normal numbers in base $2$ are of the form $ND_N\ll\log^2 N$. The first example is due to Levin (1999), which was later generalized by Becher and Carton (2019). In this talk we discuss the recent result in joint work with Gerhard Larcher that guarantees $ND_N\gg \log^2 N$ for Levin's binary normal number. So EITHER $ND_N\ll \log^2N$ is the best possible order for $D_N$ in $N$ of a normal number OR there exist another example of a binary normal number with a better growth of $ND_N$ in $N$. The recent result for Levin's normal number might support the conjecture that $ND_N\ll \log^2N$ is the best order for $D_N$ in $N$ a normal number can obtain.

#### Année 2022

One world numeration seminar

Mardi 13 décembre 2022, 14 heures, Online

**Hiroki Takahasi** (Keio University) *Distribution of cycles for one-dimensional random dynamical systems*

This talk is based on the preprint arXiv:2108.05522. If time permits, I will mention some future perspectives in this project.

One world numeration seminar

Mardi 6 décembre 2022, 14 heures, Online

**Christoph Bandt** (Universität Greifswald) *Automata generated topological spaces and self-affine tilings*

One world numeration seminar

Mardi 29 novembre 2022, 14 heures, Online

**Manuel Hauke** (TU Graz) *The asymptotic behaviour of Sudler products*

For Lebesgue-almost every $\alpha$, we can prove more: we show that for every non-decreasing function $\psi: (0,\infty) \to (0,\infty)$ with $\sum_{k=1}^{\infty} \frac{1}{\psi(k)} = \infty$ and $\liminf_{k \to \infty} \psi(k)/(k \log k)$ sufficiently large, the conditions $\log P_N(\alpha) \leq -\psi(\log N)$, $\log P_N(\alpha) \geq \psi(\log N)$ hold on sets of upper density $1$ respectively $1/2$.

One world numeration seminar

Mardi 22 novembre 2022, 14 heures, Online

**Faustin Adiceam** (Université Paris-Est Créteil) *Badly approximable vectors and Littlewood-type problems*

After outlining some of the latest developments in this very active area of research, we will take an interest in the Littlewood conjecture (c. 1930) and in its variants which all admit a natural formulation in terms of properties satisfied by badly approximable vectors. We will then show how ideas emerging from the mathematical theory of quasicrystals, from numeration systems and from the theory of aperiodic tilings have recently been used to refute the so-called t-adic Littlewood conjecture.

All necessary concepts will be defined in the talk. Joint with Fred Lunnon (Maynooth) and Erez Nesharim (Technion, Haifa).

One world numeration seminar

Mardi 15 novembre 2022, 14 heures, Online

**Seul Bee Lee** (Institute for Basic Science) *Regularity properties of Brjuno functions associated with by-excess, odd and even continued fractions*

One world numeration seminar

Mardi 8 novembre 2022, 14 heures, Online

**Wen Wu** (South China University of Technology) *From the Thue-Morse sequence to the apwenian sequences*

One world numeration seminar

Mardi 25 octobre 2022, 14 heures, Online

**Álvaro Bustos-Gajardo** (The Open University) *Quasi-recognizability and continuous eigenvalues of torsion-free S-adic systems*

Using these notions we give S-adic analogues of the notions of column number and height for substitutions, including dynamical and combinatorial interpretations of each, and give a general characterisation of the maximal equicontinuous factor of the identified family of S-adic shifts, showing as a consequence that in this context all continuous eigenvalues must be rational. As well, we employ the tools developed for a first approach to the measurable case.

This is a joint work with Neil Mañibo and Reem Yassawi.

One world numeration seminar

Mardi 18 octobre 2022, 14 heures, Online

**Yufei Chen** (TU Delft) *Matching of orbits of certain N-expansions with a finite set of digits*

One world numeration seminar

Mardi 11 octobre 2022, 14 heures, Online

**Lukas Spiegelhofer** (Montanuniversität Leoben) *Primes as sums of Fibonacci numbers*

This is joint work with Michael Drmota and Clemens Müllner (TU Wien).

One world numeration seminar

Mardi 4 octobre 2022, 14 heures, Online

**David Siukaev** (Higher School of Economics) *Exactness and Ergodicity of Certain Markovian Multidimensional Fraction Algorithms*

In 2013 T. Miernowski and A. Nogueira proved that the Euclidean algorithm and the non-homogeneous Rauzy induction satisfy the intersection property and, as a consequence, are exact. At the end of the article it is stated that other non-homogeneous markovian algorithms (Selmer, Brun and Jacobi-Perron) also satisfy the intersection property and they also exact. However, there is no proof of this. In our paper this proof is obtained by using the structure of the proof of the exactness of the Euclidean algorithm with its generalization and refinement for multidimensional algorithms. We obtained technically complex proofs that differ from the proofs given in the article of T. Miernowski and A. Nogueira by the difficulties of generalization to the multidimensional case.

One world numeration seminar

Mardi 4 octobre 2022, 14 heures 30, Online

**Alexandra Skripchenko** (Higher School of Economics) *Bruin-Troubetzkoy family of interval translation mappings: a new glance*

We suggest an alternative proof of the first statement and get a stronger version of the second one. It is a joint work in progress with Mauro Artigiani and Pascal Hubert.

One world numeration seminar

Mardi 27 septembre 2022, 14 heures, Online

**Niels Langeveld** (Montanuniversität Leoben) *$N$-continued fractions and $S$-adic sequences*

One world numeration seminar

Mardi 13 septembre 2022, 14 heures 30, Online

**Benedict Sewell** (Alfréd Rényi Institute) *An upper bound on the box-counting dimension of the Rauzy gasket*

One world numeration seminar

Mardi 12 juillet 2022, 14 heures 30, Online

**Ruofan Li** (South China University of Technology) *Rational numbers in ×b-invariant sets*

One world numeration seminar

Mardi 5 juillet 2022, 14 heures 30, Online

**Charlene Kalle** (Universiteit Leiden) *Random Lüroth expansions*

One world numeration seminar

Mardi 21 juin 2022, 14 heures 30, Online

**James A. Yorke** (University of Maryland) *Large and Small Chaos Models*

One world numeration seminar

Mardi 7 juin 2022, 14 heures 30, Online

**Sophie Morier-Genoud** (Université Reims Champagne Ardenne) *q-analogues of real numbers*

One world numeration seminar

Mardi 31 mai 2022, 14 heures 30, Online

**Verónica Becher** (Universidad de Buenos Aires & CONICET Argentina) *Poisson generic real numbers*

This is joint work Nicolás Álvarez and Martín Mereb.

One world numeration seminar

Mardi 24 mai 2022, 14 heures 30, Online

**Émilie Charlier** (Université de Liège) *Spectrum, algebraicity and normalization in alternate bases*

This is joint work with Célia Cisternino, Zuzana Masáková and Edita Pelantová.

One world numeration seminar

Mardi 17 mai 2022, 14 heures 30, Online

**Vilmos Komornik** (Université de Strasbourg et Shenzhen University) *Topology of univoque sets in real base expansions*

One world numeration seminar

Mardi 3 mai 2022, 14 heures 30, Online

**Nicolas Chevallier** (Université de Haute Alsace) *Best Diophantine approximations in the complex plane with Gaussian integers*

One world numeration seminar

Mardi 19 avril 2022, 14 heures 30, Online

**Paulina Cecchi Bernales** (Universidad de Chile) *Coboundaries and eigenvalues of finitary S-adic systems*

This is joint work with Valérie Berthé and Reem Yassawi.

One world numeration seminar

Mardi 12 avril 2022, 14 heures 30, Online

**Eda Cesaratto** (Univ. Nac. de Gral. Sarmiento & CONICET, Argentina) *Lochs-type theorems beyond positive entropy*

This is joint work with Valérie Berthé (IRIF), Pablo Rotondo (U. Gustave Eiffel) and Martín Safe (Univ. Nac. del Sur & CONICET, Argentina).

One world numeration seminar

Mardi 5 avril 2022, 14 heures 30, Online

**Jungwon Lee** (University of Warwick) *Dynamics of Ostrowski skew-product: Limit laws and Hausdorff dimensions*

One world numeration seminar

Mardi 29 mars 2022, 14 heures 30, Online

**Tingyu Zhang** (East China Normal University) *Random β-transformation on fat Sierpiński gasket*

This is joint work with K. Dajani and W. Li.

One world numeration seminar

Mardi 15 mars 2022, 14 heures 30, Online

**Pierre Popoli** (Université de Lorraine) *Maximum order complexity for some automatic and morphic sequences along polynomial values*

One world numeration seminar

Mardi 8 mars 2022, 14 heures 30, Online

**Michael Coons** (Universität Bielefeld) *A spectral theory of regular sequences*

One world numeration seminar

Mardi 1 mars 2022, 14 heures 30, Online

**Daniel Krenn** (Universität Salzburg) *k-regular sequences: Asymptotics and Decidability*

One world numeration seminar

Mardi 15 février 2022, 14 heures 30, Online

**Wolfgang Steiner** (IRIF) *Unique double base expansions*

This is joint work with Vilmos Komornik and Yuru Zou.

One world numeration seminar

Mardi 8 février 2022, 14 heures 30, Online

**Magdaléna Tinková** (České vysoké učení technické v Praze) *Universal quadratic forms, small norms and traces in families of number fields*

One world numeration seminar

Mardi 1 février 2022, 14 heures 30, Online

**Jonas Jankauskas** (Vilniaus universitetas) *Digit systems with rational base matrix over lattices*

One world numeration seminar

Mardi 25 janvier 2022, 14 heures 30, Online

**Claudio Bonanno** (Università di Pisa) *Infinite ergodic theory and a tree of rational pairs*

One world numeration seminar

Mardi 18 janvier 2022, 14 heures 30, Online

**Agamemnon Zafeiropoulos** (NTNU) *The order of magnitude of Sudler products*

- If $b\leq 5$, then $\liminf_{N\to \infty}P_N(\alpha) >0$ and $\limsup_{N\to \infty} P_N(\alpha)/N < \infty$.

- If $b\geq 6$, then $\liminf_{N\to \infty}P_N(\alpha) = 0$ and $\limsup_{N\to \infty} P_N(\alpha)/N = \infty$.

We also present an analogue of the previous result for arbitrary quadratic irrationals (joint work with S. Grepstad and M. Neumueller).

One world numeration seminar

Mardi 11 janvier 2022, 14 heures 30, Online

**Philipp Gohlke** (Universität Bielefeld) *Zero measure spectrum for multi-frequency Schrödinger operators*

#### Année 2021

One world numeration seminar

Mardi 21 décembre 2021, 14 heures 30, Online

**Fan Lü** (Sichuan Normal University) *Multiplicative Diophantine approximation in the parameter space of beta-dynamical system*

One world numeration seminar

Mardi 7 décembre 2021, 14 heures 30, Online

**Jamie Walton** (University of Nottingham) *Extending the theory of symbolic substitutions to compact alphabets*

One world numeration seminar

Mardi 23 novembre 2021, 14 heures 30, Online

**Sascha Troscheit** (Universität Wien) *Analogues of Khintchine's theorem for random attractors*

One world numeration seminar

Mardi 16 novembre 2021, 14 heures 30, Online

**Lucía Rossi** (Montanuniversität Leoben) *Rational self-affine tiles associated to (nonstandard) digit systems*

One world numeration seminar

Mardi 9 novembre 2021, 14 heures 30, Online

**Zhiqiang Wang** (East China Normal University) *How inhomogeneous Cantor sets can pass a point*

One world numeration seminar

Mardi 9 novembre 2021, 15 heures, Online

**Younès Tierce** (Université de Rouen Normandie) *Extensions of the random beta-transformation*

One world numeration seminar

Mardi 2 novembre 2021, 14 heures 30, Online

**Pieter Allaart** (University of North Texas) *On the existence of Trott numbers relative to multiple bases*

One world numeration seminar

Mardi 26 octobre 2021, 14 heures 30, Online

**Michael Baake** (Universität Bielefeld) *Spectral aspects of aperiodic dynamical systems*

One world numeration seminar

Mardi 19 octobre 2021, 14 heures 30, Online

**Mélodie Lapointe** (IRIF) *q-analog of the Markoff injectivity conjecture*

One world numeration seminar

Mardi 12 octobre 2021, 14 heures 30, Online

**Liangang Ma** (Binzhou University) *Inflection points in the Lyapunov spectrum for IFS on intervals*

One world numeration seminar

Mardi 5 octobre 2021, 14 heures 30, Online

**Lulu Fang** (Nanjing University of Science and Technology) *On upper and lower fast Khintchine spectra in continued fractions*

One world numeration seminar

Mardi 5 octobre 2021, 15 heures, Online

**Taylor Jones** (University of North Texas) *On the Existence of Numbers with Matching Continued Fraction and Decimal Expansion*

One world numeration seminar

Mardi 28 septembre 2021, 14 heures 30, Online

**Philipp Hieronymi** (Universität Bonn) *A strong version of Cobham's theorem*

The essence of Cobham's theorem is that recognizability depends strongly on the choice of the base k. Our results strengthens this: two non-Presburger definable sets that are recognizable in multiplicatively independent bases, are not only distinct, but together computationally intractable over Presburger arithmetic.

This is joint work with Christian Schulz.

One world numeration seminar

Mardi 21 septembre 2021, 14 heures 30, Online

**Maria Siskaki** (University of Illinois at Urbana-Champaign) *The distribution of reduced quadratic irrationals arising from continued fraction expansions*

One world numeration seminar

Mardi 14 septembre 2021, 14 heures 30, Online

**Steve Jackson** (University of North Texas) *Descriptive complexity in numeration systems*

One world numeration seminar

Mardi 7 septembre 2021, 14 heures 30, Online

**Oleg Karpenkov** (University of Liverpool) *On Hermite's problem, Jacobi-Perron type algorithms, and Dirichlet groups*

We will briefly discuss a new approach which is based on geometry of numbers. In addition we point out one important application of Jacobi-Perron type algorithms to the computation of independent elements in the maximal groups of commuting matrices of algebraic irrationalities.

One world numeration seminar

Mardi 6 juillet 2021, 14 heures 30, Online

**Niclas Technau** (University of Wisconsin - Madison) *Littlewood and Duffin-Schaeffer-type problems in diophantine approximation*

One world numeration seminar

Mardi 29 juin 2021, 14 heures 30, Online

**Polina Vytnova** (University of Warwick) *Hausdorff dimension of Gauss-Cantor sets and their applications to the study of classical Markov spectrum*

In this talk we will see how the first transition point, where the Markov spectra acquires the full measure can be computed by the means of estimating Hausdorff dimension of the certain Gauss-Cantor sets.

The talk is based on a joint work with C. Matheus, C. G. Moreira and M. Pollicott.

One world numeration seminar

Mardi 22 juin 2021, 14 heures 30, Online

**Lingmin Liao** (Université Paris-Est Créteil Val de Marne) *Simultaneous Diophantine approximation of the orbits of the dynamical systems x2 and x3*

One world numeration seminar

Mardi 15 juin 2021, 14 heures 30, Online

**Sam Chow** (University of Warwick) *Dyadic approximation in the Cantor set*

One world numeration seminar

Mardi 8 juin 2021, 14 heures 30, Online

**Shigeki Akiyama** (University of Tsukuba) *Counting balanced words and related problems*

One world numeration seminar

Mardi 1 juin 2021, 14 heures 30, Online

**Bastián Espinoza** (Université de Picardie Jules Verne and Universidad de Chile) *Automorphisms and factors of finite topological rank systems*

One world numeration seminar

Mardi 25 mai 2021, 14 heures 30, Online

**Charles Fougeron** (IRIF) *Dynamics of simplicial systems and multidimensional continued fraction algorithms*

Starting from the classical case of Farey's algorithm, which is an “additive” version of Gauss's algorithm, I will present a combinatorial point of view on these algorithms which allows to us to use a random walk approach. In this model, taking a random vector for the Lebesgue measure will correspond to following a random walk with memory in a labelled graph called symplicial system. The laws of probability for this random walk are elementary and we can thus develop probabilistic techniques to study their generic dynamical behaviour. This will lead us to describe a purely graph theoretic criterion to check the convergence of a continued fraction algorithm.

One world numeration seminar

Mardi 18 mai 2021, 14 heures 30, Online

**Joseph Vandehey** (University of Texas at Tyler) *Solved and unsolved problems in normal numbers*

One world numeration seminar

Mardi 11 mai 2021, 14 heures 30, Online

**Giulio Tiozzo** (University of Toronto) *The bifurcation locus for numbers of bounded type*

We study how the set B(t) changes as the parameter t ranges in [0,1], and describe precisely the bifurcations that occur as the parameters change. Further, we discuss continuity properties of the Hausdorff dimension of B(t) and its regularity.

Finally, we establish a precise correspondence between these bifurcations and the bifurcations for the classical family of real quadratic polynomials.

Joint with C. Carminati.

One world numeration seminar

Mardi 4 mai 2021, 16 heures, Online

**Tushar Das** (University of Wisconsin - La Crosse) *Hausdorff Hensley Good & Gauss*

One world numeration seminar

Mardi 27 avril 2021, 14 heures 30, Online

**Boris Adamczewski** (CNRS, Université Claude Bernard Lyon 1) *Expansions of numbers in multiplicatively independent bases: Furstenberg's conjecture and finite automata*

One world numeration seminar

Mardi 20 avril 2021, 14 heures 30, Online

**Ayreena Bakhtawar** (La Trobe University) *Metrical theory for the set of points associated with the generalized Jarnik-Besicovitch set*

One world numeration seminar

Mardi 13 avril 2021, 14 heures 30, Online

**Andrew Mitchell** (University of Birmingham) *Measure theoretic entropy of random substitutions*

One world numeration seminar

Mardi 30 mars 2021, 14 heures 30, Online

**Michael Drmota** (TU Wien) *(Logarithmic) Densities for Automatic Sequences along Primes and Squares*

The purpose of this talk is to present a corresponding result for subsequences of general automatic sequences along primes and squares. This is a far reaching generalization of two breakthrough results of Mauduit and Rivat from 2009 and 2010, where they solved two conjectures by Gelfond on the densities of 0 and 1 of t(p_n) and t(n^2) (where p_n denotes the sequence of primes).

More technically, one has to develop a method to transfer density results for primitive automatic sequences to logarithmic-density results for general automatic sequences. Then as an application one can deduce that the logarithmic densities of any automatic sequence along squares (n^2)_{n≥0} and primes (p_n)_{n≥1} exist and are computable. Furthermore, if densities exist then they are (usually) rational.

This is a joint work with Boris Adamczewski and Clemens Müllner.

One world numeration seminar

Mardi 23 mars 2021, 14 heures 30, Online

**Godofredo Iommi** (Pontificia Universidad Católica de Chile) *Arithmetic averages and normality in continued fractions*

One world numeration seminar

Mardi 16 mars 2021, 14 heures 30, Online

**Alexandra Skripchenko** (Higher School of Economics) *Double rotations and their ergodic properties*

The talk is based on a joint work with Mauro Artigiani, Charles Fougeron and Pascal Hubert.

One world numeration seminar

Mardi 9 mars 2021, 14 heures 30, Online

**Natalie Priebe Frank** (Vassar College) *The flow view and infinite interval exchange transformation of a recognizable substitution*

In this talk I'll explain how it all works and state some results and questions. There will be pictures.

One world numeration seminar

Mardi 2 mars 2021, 16 heures, Online

**Vitaly Bergelson** (Ohio State University) *Normal sets in (ℕ,+) and (ℕ,×)*

One world numeration seminar

Mardi 23 février 2021, 14 heures 30, Online

**Seulbee Lee** (Scuola Normale Superiore di Pisa) *Odd-odd continued fraction algorithm*

One world numeration seminar

Mardi 16 février 2021, 14 heures 30, Online

**Gerardo González Robert** (Universidad Nacional Autónoma de México) *Good's Theorem for Hurwitz Continued Fractions*

One world numeration seminar

Mardi 9 février 2021, 14 heures 30, Online

**Clemens Müllner** (TU Wien) *Multiplicative automatic sequences*

One world numeration seminar

Mardi 2 février 2021, 14 heures 30, Online

**Samuel Petite** (Université de Picardie Jules Verne) *Interplay between finite topological rank minimal Cantor systems, S-adic subshifts and their complexity*

One world numeration seminar

Mardi 26 janvier 2021, 14 heures 30, Online

**Carlo Carminati** (Università di Pisa) *Prevalence of matching for families of continued fraction algorithms: old and new results*

Our main focus will be the matching property for the family of Ito-Tanaka continued fractions: we will discuss the analogies with Nakada's case (such as prevalence of matching), but also some unexpected features which are peculiar of this case.

The core of the talk is about some recent results obtained in collaboration with Niels Langeveld and Wolfgang Steiner.

One world numeration seminar

Mardi 19 janvier 2021, 14 heures 30, Online

**Tom Kempton** (University of Manchester) *Bernoulli Convolutions and Measures on the Spectra of Algebraic Integers*

\Sigma(\beta) := \{ \sum_{i=1}^n a_i \beta^i : n \in \mathbb{N}, a_i \in A \}.

In the case that beta is Pisot one can study the spectrum of beta dynamically using substitutions or cut and project schemes, and this allows one to see lots of local structure in the spectrum. There are higher dimensional analogues for other algebraic integers. In this talk we will define a random walk on the spectrum of beta and show how, with appropriate renormalisation, this leads to an infinite stationary measure on the spectrum. This measure has local structure analagous to that of the spectrum itself. Furthermore, this measure has deep links with the Bernoulli convolution, and in particular new criteria for the absolute continuity of Bernoulli convolutions can be stated in terms of the ergodic properties of these measures.

One world numeration seminar

Mardi 5 janvier 2021, 14 heures 30, Online

**Claire Merriman** (Ohio State University) *alpha-odd continued fractions*

This talk is based on joint work with Florin Boca and animations done by Xavier Ding, Gustav Jennetten, and Joel Rozhon as part of an Illinois Geometry Lab project.

#### Année 2020

One world numeration seminar

Mardi 15 décembre 2020, 14 heures 30, Online

**Lukas Spiegelhofer** (Montanuniversität Leoben) *The digits of n+t*

(1) Do we have c_t = δ(0,t) + δ(1,t) + … > 1/2? This is a conjecture due to T. W. Cusick (2011).

(2) What does the probability distribution defined by k → δ(k,t) look like?

We prove that indeed c_t > 1/2 if the binary expansion of t contains at least M blocks of contiguous ones, where M is effective. Our second theorem states that δ(j,t) usually behaves like a normal distribution, which extends a result by Emme and Hubert (2018).

This is joint work with Michael Wallner (TU Wien).

One world numeration seminar

Mardi 8 décembre 2020, 14 heures 30, Online

**Tanja Isabelle Schindler** (Scuola Normale Superiore di Pisa) *Limit theorems on counting large continued fraction digits*

One world numeration seminar

Mardi 1 décembre 2020, 14 heures 30, Online

**Michael Barnsley** (Australian National University) *Rigid fractal tilings*

One world numeration seminar

Mardi 17 novembre 2020, 14 heures 30, Online

**Jacques Sakarovitch** (IRIF, CNRS et Télécom Paris) *The carry propagation of the successor function*

In the case of the usual base p numeration system, it can be shown that the limit indeed exists and is equal to p/(p-1). We recover a similar value for those numeration systems we consider and for which the limit exists. The problem is less the computation of the carry propagation than the proof of its existence. We address it for various kinds of numeration systems: abstract numeration systems, rational base numeration systems, greedy numeration systems and beta-numeration. This problem is tackled with three different types of techniques: combinatorial, algebraic, and ergodic, each of them being relevant for different kinds of numeration systems.

This work has been published in Advances in Applied Mathematics 120 (2020). In this talk, we shall focus on the algebraic and ergodic methods.

Joint work with V. Berthé (Irif), Ch. Frougny (Irif), and M. Rigo (Univ. Liège).

One world numeration seminar

Mardi 10 novembre 2020, 14 heures 30, Online

**Pieter Allaart** (University of North Texas) *On the smallest base in which a number has a unique expansion*

One world numeration seminar

Mardi 3 novembre 2020, 14 heures 30, Online

**Tomáš Vávra** (University of Waterloo) *Distinct unit generated number fields and finiteness in number systems*

One world numeration seminar

Mardi 27 octobre 2020, 14 heures 30, Online

**Mélodie Andrieu** (Aix-Marseille University) *A Rauzy fractal unbounded in all directions of the plane*

One world numeration seminar

Mardi 20 octobre 2020, 14 heures 30, Online

**Paul Surer** (University of Natural Resources and Life Sciences, Vienna) *Representations for complex numbers with integer digits*

One world numeration seminar

Mardi 13 octobre 2020, 14 heures 30, Online

**Kan Jiang** (Ningbo University) *Representations of real numbers on fractal sets*

One world numeration seminar

Mardi 6 octobre 2020, 14 heures 30, Online

**Francesco Veneziano** (University of Genova) *Finiteness and periodicity of continued fractions over quadratic number fields*

One world numeration seminar

Mardi 29 septembre 2020, 14 heures 30, Online

**Marta Maggioni** (Leiden University) *Random matching for random interval maps*

One world numeration seminar

Mardi 22 septembre 2020, 14 heures 30, Online

**Yotam Smilansky** (Rutgers University) *Multiscale Substitution Tilings*

One world numeration seminar

Mardi 15 septembre 2020, 14 heures 30, Online

**Jeffrey Shallit** (University of Waterloo) *Lazy Ostrowski Numeration and Sturmian Words*

One world numeration seminar

Mardi 8 septembre 2020, 14 heures 30, Online

**Bing Li** (South China University of Technology) *Some fractal problems in beta-expansions*

One world numeration seminar

Mardi 1 septembre 2020, 14 heures 30, Online

**Bill Mance** (Adam Mickiewicz University in Poznań) *Hotspot Lemmas for Noncompact Spaces*

One world numeration seminar

Mardi 14 juillet 2020, 14 heures 30, Online

**Attila Pethő** (University of Debrecen) *On diophantine properties of generalized number systems - finite and periodic representations*

One world numeration seminar

Mardi 7 juillet 2020, 14 heures 30, Online

**Hajime Kaneko** (University of Tsukuba) *Analogy of Lagrange spectrum related to geometric progressions*

One world numeration seminar

Mardi 30 juin 2020, 14 heures 30, Online

**Niels Langeveld** (Leiden University) *Continued fractions with two non integer digits*

One world numeration seminar

Mardi 23 juin 2020, 14 heures 30, Online

**Derong Kong** (Chongqing University) *Univoque bases of real numbers: local dimension, Devil's staircase and isolated points*

One world numeration seminar

Mardi 16 juin 2020, 14 heures 30, Online

**Carlos Matheus** (CNRS, École Polytechnique) *Approximations of the Lagrange and Markov spectra*

One world numeration seminar

Mardi 9 juin 2020, 14 heures 30, Online

**Simon Baker** (University of Birmingham) *Equidistribution results for self-similar measures*

One world numeration seminar

Mardi 2 juin 2020, 14 heures 30, Online

**Henna Koivusalo** (University of Vienna) *Linear repetition in polytopal cut and project sets*

One world numeration seminar

Mardi 26 mai 2020, 14 heures 30, Online

**Célia Cisternino** (University of Liège) *Ergodic behavior of transformations associated with alternate base expansions*

One world numeration seminar

Mardi 19 mai 2020, 14 heures 30, Online

**Boris Solomyak** (University of Bar-Ilan) *On singular substitution Z-actions*

One world numeration seminar

Mardi 12 mai 2020, 14 heures 30, Online

**Olivier Carton** (Université de Paris) *Preservation of normality by selection*

One world numeration seminar

Mardi 5 mai 2020, 14 heures 30, Online

**Narad Rampersad** (University of Winnipeg) *Ostrowski numeration and repetitions in words*