English

Quartic residues and sums involving $\binom{4k}{2k}$

Number Theory 2013-12-03 v2

Abstract

Let pp be an odd prime and let m≢0(modp)m\not\equiv 0\pmod p be a rational p-adic integer. In this paper we reveal the connection between quartic residues and the sum k=0[p/4](4k2k)1mk\sum_{k=0}^{[p/4]}\binom{4k}{2k}\frac 1{m^k}, where [x][x] is the greatest integer not exceeding xx. Let qq be a prime of the form 4k+14k+1 and so q=a2+b2q=a^2+b^2 with a,bZa,b\in\Bbb Z. When pab(a2b2)qp\nmid ab(a^2-b^2)q, we show that for r=0,1,2,3r=0,1,2,3, pq14(ab)r(modq)p^{\frac{q-1}4}\equiv (\frac ab)^r\pmod q if and only if k=0[p/4](4k2k)(a216q)k(1)p218a+p12q14(pq)(ab)r(modp),\sum_{k=0}^{[p/4]}\binom{4k}{2k}\Big(\frac{a^2}{16q}\Big)^k\equiv (-1)^{\frac{p^2-1}8a+\frac{p-1}2\cdot \frac{q-1}4}\Big(\frac pq\Big) \Big(\frac ab\Big)^r\pmod p, where (pq)(\frac pq) is the Legendre symbol. We also establish congruences for k=0[p/4](4k2k)1mk(modp)\sum_{k=0}^{[p/4]}\binom{4k}{2k}\frac 1{m^k}\pmod p in the cases m=17,18,20,32,52,80,272m=17,18,20,32,52,80,272.

Keywords

Cite

@article{arxiv.1311.6364,
  title  = {Quartic residues and sums involving $\binom{4k}{2k}$},
  author = {Zhi-Hong Sun},
  journal= {arXiv preprint arXiv:1311.6364},
  year   = {2013}
}

Comments

Section 3 is new

R2 v1 2026-06-22T02:14:25.589Z