1. Lambert series of logarithm, the derivative of Deninger's function $R(z),$ and a mean value theorem for $\zeta \left (\frac {1}{2}-it\right)\zeta '\left (\frac {1}{2}+it\right)$.
- Author
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Banerjee, Soumyarup, Dixit, Atul, and Gupta, Shivajee
- Subjects
LOGARITHMS ,DERIVATIVES (Mathematics) ,MEAN value theorems ,ASYMPTOTIC expansions ,NUMERICAL analysis - Abstract
An explicit transformation for the series $\sum \limits _{n=1}^{\infty }\displaystyle \frac {\log (n)}{e^{ny}-1}$ , or equivalently, $\sum \limits _{n=1}^{\infty }d(n)\log (n)e^{-ny}$ for Re $(y)>0$ , which takes y to $1/y$ , is obtained for the first time. This series transforms into a series containing the derivative of $R(z)$ , a function studied by Christopher Deninger while obtaining an analog of the famous Chowla–Selberg formula for real quadratic fields. In the course of obtaining the transformation, new important properties of $\psi _1(z)$ (the derivative of $R(z)$) are needed as is a new representation for the second derivative of the two-variable Mittag-Leffler function $E_{2, b}(z)$ evaluated at $b=1$ , all of which may seem quite unexpected at first glance. Our transformation readily gives the complete asymptotic expansion of $\sum \limits _{n=1}^{\infty }\displaystyle \frac {\log (n)}{e^{ny}-1}$ as $y\to 0$ which was also not known before. An application of the latter is that it gives the asymptotic expansion of $ \displaystyle \int _{0}^{\infty }\zeta \left (\frac {1}{2}-it\right)\zeta '\left (\frac {1}{2}+it\right)e^{-\delta t}\, dt$ as $\delta \to 0$. [ABSTRACT FROM AUTHOR]
- Published
- 2024
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