Convergence exponent of Dirichlet non-improvable numbers in the theory of continued fractions

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Hauptverfasser: Tan, Xiaoyan, Zhang, Zhenliang
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Veröffentlicht: 2025
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author Tan, Xiaoyan
Zhang, Zhenliang
author_facet Tan, Xiaoyan
Zhang, Zhenliang
contents Let $x \in [0,1)$ be an irrational number with continued fraction expansion $[a_1(x),a_2(x), \cdots,a_n(x),\cdots]$ and $q_n(x)$ be the denominator of its $n$-th convergent. We establish, for any $α,β$ in $[0,+\infty]$, the Hausdorff dimension formula of the intersections of the sets of Dirichlet non-improvable numbers and the level set of convergent exponent, i.e. $$ G(α,β): =\left\{x\in[0,1)\colon τ(x)=α,\,\,\text{and} \,\, \limsup_{n\to\infty}\frac{\log (a_n(x)a_{n+1}(x))}{\log q_n(x)}\geqβ\right\}, $$ and $$ E(α,β): =\left\{x\in[0,1)\colon τ(x)=α,\,\,\text{and} \,\, \limsup_{n\to\infty}\frac{\log (a_n(x)a_{n+1}(x))}{\log q_n(x)}=β\right\}, $$ where $$ τ(x):= \inf\Big\{s \geq 0: \sum_{n \geq 1} a^{-s}_n(x)<\infty\Big\}. $$
format Preprint
id arxiv_https___arxiv_org_abs_2509_23059
institution arXiv
publishDate 2025
record_format arxiv
spellingShingle Convergence exponent of Dirichlet non-improvable numbers in the theory of continued fractions
Tan, Xiaoyan
Zhang, Zhenliang
Number Theory
11K55, 28A80
Let $x \in [0,1)$ be an irrational number with continued fraction expansion $[a_1(x),a_2(x), \cdots,a_n(x),\cdots]$ and $q_n(x)$ be the denominator of its $n$-th convergent. We establish, for any $α,β$ in $[0,+\infty]$, the Hausdorff dimension formula of the intersections of the sets of Dirichlet non-improvable numbers and the level set of convergent exponent, i.e. $$ G(α,β): =\left\{x\in[0,1)\colon τ(x)=α,\,\,\text{and} \,\, \limsup_{n\to\infty}\frac{\log (a_n(x)a_{n+1}(x))}{\log q_n(x)}\geqβ\right\}, $$ and $$ E(α,β): =\left\{x\in[0,1)\colon τ(x)=α,\,\,\text{and} \,\, \limsup_{n\to\infty}\frac{\log (a_n(x)a_{n+1}(x))}{\log q_n(x)}=β\right\}, $$ where $$ τ(x):= \inf\Big\{s \geq 0: \sum_{n \geq 1} a^{-s}_n(x)<\infty\Big\}. $$
title Convergence exponent of Dirichlet non-improvable numbers in the theory of continued fractions
topic Number Theory
11K55, 28A80
url https://arxiv.org/abs/2509.23059