Arakawa–Kaneko zeta function
# Arakawa–Kaneko zeta function

In mathematics, the Arakawa–Kaneko zeta function is a generalisation of the Riemann zeta function which generates special values of the polylogarithm function.

## Definition

The zeta function $\xi _{k}(s)$ is defined by

    $\xi _{k}(s)={\frac {1}{\Gamma (s)}}\int _{0}^{+\infty }{\frac {t^{s-1}}{e^{t}-1}}\mathrm {Li} _{k}(1-e^{-t})\,dt\$

where $Li_k$ is the k-th polylogarithm

    $\mathrm {Li} _{k}(z)=\sum _{n=1}^{\infty }{\frac {z^{n}}{n^{k}}}\ .$

## Properties

The integral converges for $\Re (s)>0$ and $\xi _{k}(s)$ has analytic continuation to the whole complex plane as an entire function.

The special case k = 1 gives $\xi _{1}(s)=s\zeta (s+1)$ where $\zeta$ is the Riemann zeta-function.

The special case s = 1 remarkably also gives $\xi _{k}(1)=\zeta (k+1)$ where $\zeta$ is the Riemann zeta-function.

The values at integers are related to multiple zeta function values by

    $\xi _{k}(m)=\zeta _{m}^{*}(k,1,\ldots ,1)$

where

    $\zeta _{n}^{*}(k_{1},\dots ,k_{n-1},k_{n})=\sum _{0<m_{1}<m_{2}<\cdots <m_{n}}{\frac {1}{m_{1}^{k_{1}}\cdots m_{n-1}^{k_{n-1}}m_{n}^{k_{n}}}}\ .$
