Bessel J

The Bessel functions of the first kind, $J_{\nu} \colon \mathbb{C} \rightarrow \mathbb{C}$ are defined by $$J_{\nu}(z)=\displaystyle\sum_{k=0}^{\infty} \dfrac{(-1)^k}{k! \Gamma(k+\nu+1)2^{2k+\nu}}z^{2k+\nu},$$ where $\Gamma$ denotes the gamma function.