\[e^{-\frac{1}{2}y}\left(\frac{x+y}{x}\right)^{\kappa}\sum_{n=0}^{\infty}\frac{{%
\left(\frac{1}{2}+\mu-\kappa\right)_{n}}{\left(\frac{1}{2}-\mu-\kappa\right)_{%
n}}}{n!}\*\left(\frac{y}{x+y}\right)^{n}W_{\kappa-n,\mu}\left(x\right),\]