English

Fast formulas for the Hurwitz values $\zeta(2,a)$ and $\zeta(3,a)$

Number Theory 2025-12-10 v5

Abstract

We prove two fast formulas for the Hurwitz values ζ(2,a)\zeta(2,a) and ζ(3,a)\zeta(3,a) respectively with the help of the WZ method. In them (a)n(a)_n denotes the rising factorial or Pochhammer's symbol defined by (a)0=1(a)_0=1 and (a)n=a(a+1)(a+n1)(a)_n=a(a+1)\cdots(a+n-1) for positive integers nn. The Huwitz ζ\zeta function is defined by ζ(s,a)=ζ(0,s,a)=k=0(k+a)s\zeta(s,a)=\zeta(0,s,a)=\sum_{k=0}^{\infty} (k+a)^{-s}. In addition, we can use these fast evaluations to compute also in a rapid way Dirichlet values of the kinds Lχ(2)L_{\chi}(2) and Lχ(3)L_{\chi}(3).

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Cite

@article{arxiv.2504.01975,
  title  = {Fast formulas for the Hurwitz values $\zeta(2,a)$ and $\zeta(3,a)$},
  author = {Jesús Guillera},
  journal= {arXiv preprint arXiv:2504.01975},
  year   = {2025}
}

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7 pages