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2024/104/1-2 (12) — DOI: 10.5486/PMD.2024.9691 — pp. 221-230

On the denominators of generalized harmonic numbers. II

Authors: Bing-Ling Wu Orcid.org link for Bing-Ling Wu and Xiao-Hui Yan Orcid.org link for Xiao-Hui Yan

Abstract:

For three positive integers $a$, $b$ and $n$, let $H_{a,b}(n)$ be the sum of the reciprocals of the first $n$ terms of arithmetic progression $\{ak+b:k=0,1,\dots\}$, and let $v_{a,b}(n)$ be the denominator of $H_{a,b}(n)$. In this paper, we prove that the set of positive integers $n$ satisfying $\nu_p(v_{a,b}(n))=\nu_p([b,b+a,\dots,b+(n-1)a])$ has positive logarithmic density, where $[b,b+a,\dots,b+(n-1)a]$ denotes the least common multiple of $b,b+a,\dots,b+(n-1)a$.

Keywords: harmonic number, generalized harmonic number, $p$-adic valuation, arithmetic progression, Eswarathasan—Levine conjecture, asymptotic density, logarithmic density

Mathematics Subject Classification: 11B05, 11B25, 11B75