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JOURNALS // Matematicheskii Sbornik // Archive

Mat. Sb., 2026 Volume 217, Number 1, Pages 54–88 (Mi sm10170)

Modular values of continuants with fixed prefixes and endings

I. D. Kan

Moscow Aviation Institute (National Research University), Moscow, Russia

Abstract: Consider the set of finite words in a finite alphabet $\mathbf{A}\subseteq\mathbb{N}$. Add a prefix $V$ and an ending $W$, which are some fixed finite words in the alphabet $\mathbb{N}$, to each word. We interpret the resulting words as the expansions in finite continued fractions of some rational numbers in the interval $(0,1)$. Next consider the irreducible denominators of these rational numbers; we denote the set of those denominators that do not exceed some quantity $N\in \mathbb{N}$ (which is an increasing parameter) by $\mathfrak{D}^{N}_{\mathbf{A},V,W}$. We prove that under certain conditions on $\mathbf{A}$, $V$ and $W$, for each prime number $Q$ proportional to a fixed fractional power of $N$ the set $\mathfrak{D}^{N}_{\mathbf{A},V,W}$ contains almost all possible residues modulo $Q$, and the remainder in this asymptotic formula involves a power reduction with respect to $Q$.

Keywords: trigonometric sum, Zaremba's conjecture, Hausdorff dimension, continued fraction, continuant, Keywo ensemble.

PACS: 11A55

Received: 11.08.2024 and 12.07.2025

DOI: 10.4213/sm10170



© Steklov Math. Inst. of RAS, 2026