Metrical properties for the large partial quotients with product forms in continued fractions

Abstract

The metrical theory of the product of consecutive partial quotients is associated with the uniform Diophantine approximation, specifically to the improvements to Dirichlet's theorem. Achieving some variant forms of metrical theory in continued fractions, we study the distribution of the at least two large partial quotients with product forms among the first $n$ terms. More precisely, let $[a_1(x),a_2(x),\ldots]$ be the continued fraction expansion of an irrational number $x\in(0,1),$ and let $\varphi\colon \N\to\R$ be a non-decreasing function, we completely determine the size of the set \begin{align*} \mathcal{F}_2(\varphi)=\Big\{x\in[0,1)\colon \exists ~1\le k\neq l \le n, ~&a_{k}(x)a_{k+1}(x)\ge \varphi(n), \\&a_{l}(x)a_{l+1}(x)\ge \varphi(n) \text{ for infinitely many } n\in \N \Big\} \end{align*} in terms of Lebesgue measure and Hausdorff dimension.