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Asymptotic behavior for the sum of partial quotients in continued fraction expansions

Published online by Cambridge University Press:  11 September 2025

Xiao Chen
Affiliation:
School of Mathematics and Statistics, https://ror.org/00xp9wg62 Nanjing University of Science and Technology , Nanjing 210094, China e-mail: 922130830116@njust.edu.cn mathli@njust.edu.cn very.zeng@outlook.com
Junjie Li
Affiliation:
School of Mathematics and Statistics, https://ror.org/00xp9wg62 Nanjing University of Science and Technology , Nanjing 210094, China e-mail: 922130830116@njust.edu.cn mathli@njust.edu.cn very.zeng@outlook.com
Lei Shang*
Affiliation:
College of Sciences, https://ror.org/05td3s095 Nanjing Agricultural University , Nanjing 210095, China
Xin Zeng
Affiliation:
School of Mathematics and Statistics, https://ror.org/00xp9wg62 Nanjing University of Science and Technology , Nanjing 210094, China e-mail: 922130830116@njust.edu.cn mathli@njust.edu.cn very.zeng@outlook.com

Abstract

Let $[a_1(x),a_2(x),a_3(x),\dots ]$ be the continued fraction expansion of an irrational number $x\in (0,1)$. Denote by $S_{n}(x):=\sum _{k=1}^{n} a_{k}(x)$ the sum of partial quotients of x. From the results of Khintchine (1935), Diamond and Vaaler (1986), and Philipp (1988), it follows that for Lebesgue almost every $x \in (0,1)$,

$$\begin{align*}\liminf _{n \rightarrow \infty} \frac{S_{n}(x)}{n \log n}=\frac{1}{\log 2} \quad \text {and} \quad \limsup _{n \rightarrow \infty} \frac{S_{n}(x)}{n \log n}=\infty. \end{align*}$$
We investigate the Baire category and Hausdorff dimension of the set of points for which the above limit inferior and limit superior assume any prescribed values. We also conduct analogous analyses for the sum of products of consecutive partial quotients.

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Article
Copyright
© The Author(s), 2025. Published by Cambridge University Press on behalf of Canadian Mathematical Society

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Footnotes

This research was supported by the Natural Science Foundation of Jiangsu Province (Grant No. BK20241541) and the National Undergraduate Training Program for Innovation and Entrepreneurship (Grant No. 202410288085Z).

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