English

A parametric congruence motivated by Orr's identity

Number Theory 2023-02-28 v2 Combinatorics

Abstract

For any m,nN={0,1,2}m,n\in\mathbb{N}=\{0,1,2\ldots\}, the truncated hypergeometric series m+1Fm{}_{m+1}F_m is defined by m+1Fm[x0x1xmy1ymz]n=k=0n(x0)k(x1)k(xm)k(y1)k(ym)kzkk!, {}_{m+1}F_m\bigg[\begin{matrix}x_0&x_1&\ldots&x_m\\ &y_1&\ldots&y_m\end{matrix}\bigg|z\bigg]_n=\sum_{k=0}^n\frac{(x_0)_k(x_1)_k\cdots(x_m)_k}{(y_1)_k\cdots(y_m)_k}\cdot\frac{z^k}{k!}, where (x)k=x(x+1)(x+k1)(x)_k=x(x+1)\cdots(x+k-1) is the Pochhammer symbol. Let pp be an odd prime. For α,zZp\alpha,z\in\mathbb{Z}_p with αp0(mod2)\langle -\alpha\rangle_p\equiv0\pmod{2}, where xp\langle x\rangle_p denotes the least nonnegative residue of xx modulo pp for any xZpx\in\mathbb{Z}_p, we mainly prove the following congruence motivated by Orr's identity: 2F1[12α3212α1z]p12F1[12α1212α1z]p13F2[α2α1211z]p1(modp2). {}_2F_1\bigg[\begin{matrix}\frac12\alpha&\frac32-\frac12\alpha\\ &1\end{matrix}\bigg|z\bigg]_{p-1}{}_2F_1\bigg[\begin{matrix}\frac12\alpha&\frac12-\frac12\alpha\\ &1\end{matrix}\bigg|z\bigg]_{p-1}\equiv{}_3F_2\bigg[\begin{matrix}\alpha&2-\alpha&\frac12\\ &1&1\end{matrix}\bigg|z\bigg]_{p-1}\pmod{p^2}. As a corollary, for any positive integer bb with p±1(modb)p\equiv\pm1\pmod{b} and 1/bp0(mod2)\langle -1/b\rangle_p\equiv0\pmod{2}, we deduce that k=0p1(b2k+b1)(2kk)4k(1/bk)(1/b1k)0(modp2). \sum_{k=0}^{p-1}(b^2k+b-1)\frac{\binom{2k}{k}}{4^k}\binom{-1/b}{k}\binom{1/b-1}{k}\equiv0\pmod{p^2}. This confirms a conjectural congruence of the second author.

Keywords

Cite

@article{arxiv.2103.02951,
  title  = {A parametric congruence motivated by Orr's identity},
  author = {Chen Wang and Zhi-Wei Sun},
  journal= {arXiv preprint arXiv:2103.02951},
  year   = {2023}
}

Comments

8 pages, accepted by Journal of Difference Equations and Applications

R2 v1 2026-06-23T23:44:48.733Z