\[\Gamma\left(a,z\right)=\frac{2z^{\frac{1}{2}a}e^{-z}}{\Gamma\left(1-a\right)}%
\int_{0}^{\infty}e^{-t}t^{-\frac{1}{2}a}K_{a}\left(2\sqrt{zt}\right)\,\mathrm{%
d}t,\]