New identities obtained from Gegenbauer series expansion

Abstract

Using the expansion in a Fourier-Gegenbauer series, we prove several identities that extend and generalize known results. In particular, it is proved among other results, that \begin{equation*} \sum_{n=0}^\infty\frac{1}{4^n}\binom{2n}{n}\frac{z-2n}{\binom{z-1/2}{n}}\binom{z}{n}^3 =\frac{\tan(\pi z)}{\pi} \end{equation*} for all complex numbers $z$ such that $\Re(z)>-\frac{1}{2}$ and $z\notin\frac{1}{2}+\mathbb{Z}$.