On a certain identity involving the Gamma function
Abstract: The goal of this paper is to prove the identity \begin{align}\sum \limits_{j=0}{\lfloor s\rfloor}\frac{(-1)j}{sj}\eta_s(j)+\frac{1}{e{s-1}ss}\sum \limits_{j=0}{\lfloor s\rfloor}(-1){j+1}\alpha_s(j)+\bigg(\frac{1-((-1){s-\lfloor s\rfloor +2}){1/(s-\lfloor s\rfloor +2)}}{2}\bigg)\nonumber \ \bigg(\sum \limits_{j=\lfloor s\rfloor +1}{\infty}\frac{(-1)j}{sj}\eta_s(j)+\frac{1}{e{s-1}ss}\sum \limits_{j=\lfloor s\rfloor +1}{\infty}(-1){j+1}\alpha_s(j)\bigg)=\frac{1}{\Gamma(s+1)},\nonumber \end{align}where \begin{align}\eta_s(j):=\bigg(e{\gamma (s-j)}\prod \limits_{m=1}{\infty}\bigg(1+\frac{s-j}{m}\bigg)\nonumber \e{-(s-j)/m}\bigg)\bigg(2+\log s-\frac{j}{s}+\sum \limits_{m=1}{\infty}\frac{s}{m(s+m)}-\sum \limits_{m=1}{\infty}\frac{s-j}{m(s-j+m)}\bigg), \nonumber \end{align}and \begin{align}\alpha_s(j):=\bigg(e{\gamma (s-j)}\prod \limits_{m=1}{\infty}\bigg(1+\frac{s-j}{m}\bigg)e{-(s-j)/m}\bigg)\bigg(\sum \limits_{m=1}{\infty}\frac{s}{m(s+m)}-\sum \limits_{m=1}{\infty}\frac{s-j}{m(s-j+m)}\bigg),\nonumber \end{align}where $\Gamma(s+1)$ is the Gamma function defined by $\Gamma(s):=\int \limits_{0}{\infty}e{-t}t{s-1}dt$ and $\gamma =\lim \limits_{n\longrightarrow \infty}\bigg(\sum \limits_{k=1}{n}\frac{1}{k}-\log n\bigg)=0.577215664\cdots $ is the Euler-Mascheroni constant.
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