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2021/98/3-4 (15) — DOI: 10.5486/PMD.2021.9023 — pp. 493-511

Three supercongruences for Apéry numbers and Franel numbers

Authors: Yong Zhang

Abstract:

The Apéry numbers $A_n$ and the Franel numbers $f_n$ are defined by $$ A_n=\sum_{k=0}^{n}{\binom{n+k}{2k}}^2{\binom{2k}{k}}^2\quad{\rm and\, }\quad f_n=\sum_{k=0}^{n}{\binom{n}{k}}^3(n=0, 1, \dots,). $$ In this paper, we prove three supercongruences for Apéry numbers and Franel numbers conjectured by Z.-W. Sun. For any prime $p\geq 5$, \begin{align*} \frac{1}{n}\left(\sum_{k=0}^{pn-1}(2k+1)A_k-p\sum_{k=0}^{n-1}(2k+1)A_k\right)&\equiv0\pmod{p^{4+3\nu_p(n)}},\\ \frac{1}{n^3}\left(\sum_{k=0}^{pn-1}(2k+1)^3A_k-p^3\sum_{k=0}^{n-1}(2k+1)^3A_k\right)&\equiv0\pmod{p^{6+3\nu_p(n)}}, \end{align*} and, for any prime $p$, $$ \frac{1}{n^3}\left(\sum_{k=0}^{pn-1}(3k+2)(-1)^kf_k-p^2\sum_{k=0}^{n-1}(3k+2)(-1)^kf_k\right)\equiv0\pmod{p^{3}},\\[-6pt] $$ where $\nu_p(n)$ denotes the $p$-adic order of $n$.

Keywords: supercongruences, Apéry numbers, Franel numbers, p-adic valuations

Mathematics Subject Classification: 11A07, 11B65, 05A10, 11B39, 11B75