English

Some new series for $1/\pi$ motivated by congruences

Number Theory 2023-02-23 v4 Combinatorics

Abstract

In this paper, we deduce a family of six new series for 1/π1/\pi; for example, n=041673840n+47771115780nWn(14441445)=14775847595π\sum_{n=0}^\infty\frac{41673840n+4777111}{5780^n}W_n\left(\frac{1444}{1445}\right) =\frac{147758475}{\sqrt{95}\,\pi} where Wn(x)=k=0n(nk)(n+kk)(2kk)(2(nk)nk)xkW_n(x)=\sum_{k=0}^n\binom nk\binom{n+k}k\binom{2k}k\binom{2(n-k)}{n-k}x^k. To do so, we transform our series to series of the type n=0an+bmnk=0n(nk)4\sum_{n=0}^\infty\frac{an+b}{m^n}\sum_{k=0}^n\binom nk^4 studied by Cooper in 2012. In addition, we pose 1717 new series for 1/π1/\pi motivated by congruences; for example, we conjecture that k=04290k+3673136k(2kk)Tk(14,1)Tk(17,16)=5390π,\sum_{k=0}^\infty\frac{4290k+367}{3136^k}\binom{2k}kT_k(14,1)T_k(17,16)=\frac{5390}{\pi}, where Tk(b,c)T_k(b,c) is the coefficient of xkx^k in the expansion of (x2+bx+c)k(x^2+bx+c)^k.

Keywords

Cite

@article{arxiv.2009.04379,
  title  = {Some new series for $1/\pi$ motivated by congruences},
  author = {Zhi-Wei Sun},
  journal= {arXiv preprint arXiv:2009.04379},
  year   = {2023}
}

Comments

20 pages.Accepted version for publication in Colloq. Math