Lambert series of logarithm, the derivative of Deninger's function $R(z)$ and a mean value theorem for $ζ\left(\frac{1}{2}-it\right)ζ'\left(\frac{1}{2}+it\right)$

Abstract

An explicit transformation for the series $\sum\limits_{n=1}^{\infty}\displaystyle\frac{\log(n)}{e^{ny}-1},$ Re$(y)>0$, which takes $y$ to $1/y$, is obtained for the first time. This series transforms into a series containing $ψ_1(z)$, the derivative of Deninger's function $R(z)$. In the course of obtaining the transformation, new important properties of $ψ_1(z)$ are derived, as is a new representation for the second derivative of the two-variable Mittag-Leffler function $E_{2, b}(z)$ evaluated at $b=1$. Our transformation readily gives the complete asymptotic expansion of $\sum\limits_{n=1}^{\infty}\displaystyle\frac{\log(n)}{e^{ny}-1}$ as $y\to0$. An application of the latter is that it gives the asymptotic expansion of $ \displaystyle\int_{0}^{\infty}ζ\left(\frac{1}{2}-it\right)ζ'\left(\frac{1}{2}+it\right)e^{-δt}\, dt$ as $δ\to0$.