English

New series involving binomial coefficients (II)

Number Theory 2026-02-09 v10 Combinatorics

Abstract

In this paper, we evaluate some series of the form k=1ak2+bk+ck(3k1)(3k2)mk(4kk).\sum_{k=1}^\infty\frac{ak^2+bk+c}{k(3k-1)(3k-2)m^k\binom{4k}k}. For example, we prove that k=1(5k24k+1)8kk(3k1)(3k2)(4kk)=32π\sum_{k=1}^\infty\frac{(5k^2-4k+1)8^{k}}{k(3k-1)(3k-2)\binom{4k}k}=\frac{3}2\pi and k=1415k2343k+62k(3k1)(3k2)(8)k(4kk)=3log2.\sum_{k=1}^\infty\frac{415k^2-343k+62}{k(3k-1)(3k-2)(-8)^k\binom{4k}k}=-3\log2. We also pose many new conjectural series identities involving binomial coefficients; for example, we conjecture that k=0(2kk)34096k(9(42k+5)0j<k1(2j+1)4+25(2k+1)3)=56π3.\sum_{k=0}^\infty\frac{\binom{2k}k^3}{4096^k}\left(9(42k+5)\sum_{0\le j<k}\frac1{(2j+1)^4}+\frac{25}{(2k+1)^3}\right)=\frac 56\pi^3.

Keywords

Cite

@article{arxiv.2307.03086,
  title  = {New series involving binomial coefficients (II)},
  author = {Zhi-Wei Sun},
  journal= {arXiv preprint arXiv:2307.03086},
  year   = {2026}
}

Comments

36 pages. Accepted by Acta Math. Sinica Engl. Series

R2 v1 2026-06-28T11:23:48.305Z