English

An analogue of Ramanujan's identity for Bernoulli-Carlitz numbers

Number Theory 2025-12-01 v4 Classical Analysis and ODEs

Abstract

In his second notebook, Ramanujan discovered the following identity for the special values of ζ(s)\zeta(s) at the odd positive integers \begin{equation*}\begin{aligned}\alpha^{-m}\,\left\{\dfrac{1}{2}\,\zeta(2m + 1) + \sum_{n = 1}^{\infty}\dfrac{n^{-2m - 1}}{e^{2\alpha n} - 1}\right\} &-(- \beta)^{-m}\,\left\{\dfrac{1}{2}\,\zeta(2m + 1) + \sum_{n = 1}^{\infty}\dfrac{n^{-2m - 1}}{e^{2\beta n} - 1}\right\}\nonumber &=2^{2m}\sum_{k = 0}^{m + 1}\dfrac{\left(-1\right)^{k-1}B_{2k}\,B_{2m - 2k+2}}{\left(2k\right)!\left(2m -2k+2\right)!}\,\alpha^{m - k + 1}\beta^k \label{(1.2)},\end{aligned} \end{equation*} where α \alpha and β \beta are positive numbers such that αβ=π2 \alpha\beta = \pi^2 and m m is a positive integer. As shown by Berndt in the viewpoint of general transformation of analytic Eisenstein series, it is a natural companion of Euler's famous formula for even zeta values. In this note, we prove an analogue of the above Ramanujan's identity in the functions fields setting, which involves the Bernoulli-Carlitz numbers.

Keywords

Cite

@article{arxiv.2309.08996,
  title  = {An analogue of Ramanujan's identity for Bernoulli-Carlitz numbers},
  author = {Su Hu and Min-Soo Kim},
  journal= {arXiv preprint arXiv:2309.08996},
  year   = {2025}
}

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14 pages, Final version