English

New series for powers of $\pi$ and related congruences

Number Theory 2020-07-17 v9 Combinatorics

Abstract

Via symbolic computation we deduce 97 new type series for powers of π\pi related to Ramanujan-type series. Here are three typical examples: k=0P(k)(2kk)(3kk)(6k3k)(k+1)(2k1)(6k1)(640320)3k=18×5574033100055π\sum_{k=0}^\infty \frac{P(k) \binom{2k}k\binom{3k}k \binom{6k}{3k}}{(k+1)(2k-1)(6k-1)(-640320)^{3k}} =\frac{18\times557403^3\sqrt{10005}}{5\pi} with \begin{align*}P(k) = &637379600041024803108 k^2 + 657229991696087780968 k \\&+ 19850391655004126179, \end{align*} k=1(3k+1)16k(2k+1)2k3(2kk)3=π282,\sum_{k=1}^\infty \frac{(3k+1)16^k}{(2k+1)^2k^3\binom{2k}k^3} = \frac{\pi^2-8}2, and n=03n+1(100)nk=0n(nk)2Tk(1,25)Tnk(1,25)=258π,\sum_{n=0}^\infty\frac{3n+1}{(-100)^n} \sum_{k=0}^n{n\choose k}^2T_k(1,25)T_{n-k}(1,25) = \frac{25}{8\pi}, where the generalized central trinomial coefficient Tk(b,c)T_k(b,c) denotes the coefficient of xkx^k in the expansion of (x2+bx+c)k(x^2+bx+c)^k. We also formulate a general characterization of rational Ramanujan-type series for 1/π1/\pi via congruences, and pose 117 new conjectural series for powers of π\pi via looking for corresponding congruences. For example, we conjecture that k=039480k+7321(29700)kTk(14,1)Tk(11,11)2=67955π.\sum_{k=0}^\infty\frac{39480k+7321}{(-29700)^k}T_k(14,1)T_k(11,-11)^2=\frac{6795\sqrt5}{\pi}. Eighteen of the new series in this paper involve some imaginary quadratic fields with class number 88.

Keywords

Cite

@article{arxiv.1911.05456,
  title  = {New series for powers of $\pi$ and related congruences},
  author = {Zhi-Wei Sun},
  journal= {arXiv preprint arXiv:1911.05456},
  year   = {2020}
}

Comments

70 pages, final published version