Summation from the viewpoint of distributions

Su Hu, Min-Soo Kim

Published 2022-10-14Version 1

Let $\{a_{1}, a_{2},\ldots, a_{n},\ldots\}$ be a sequence of complex numbers. In this paper, inspired by a recent work of Sasane, we give an explanation of the sum $$a_{1}+2a_{2}+3a_{3}+\cdots+na_{n}+\cdots,$$ and more generally, for any $k\in\mathbb{N},$ the sum $$1^{k}a_{1} +2^{k}a_{2} +3^{k}a_{3} +\cdots+n^{k}a_{n} +\cdots,$$ from the viewpoint of distributions. As applications, we explain the following summation formulas \begin{equation*} \begin{aligned} 1^{k}-2^{k}+3^{k}-\cdots&=-\frac{E_{k}(0)}{2}, \\ 1^{k}+2^{k}+3^{k}+\cdots&=-\frac{B_{k+1}}{k+1}, \\ \epsilon^{1}1^{k}+\epsilon^{2}2^{k}+\epsilon^{3}3^{k}+\cdots&=-\frac{B_{k+1}(\epsilon)}{k+1}, \end{aligned} \end{equation*} where $E_{k}(0)$, $B_{k}$ and $B_{k}(\epsilon)$ are the Euler polynomials at 0, the Bernoulli numbers and the Apostol-Bernoulli numbers, respectively.