\[E_{p}\left(z\right)=\frac{e^{-z}}{z}\sum_{s=0}^{n-1}(-1)^{s}\frac{{\left(p%
\right)_{s}}}{z^{s}}+(-1)^{n}\frac{2\pi}{\Gamma\left(p\right)}z^{p-1}F_{n+p}%
\left(z\right),\]