Upper incomplete gamma
From specialfunctionswiki
The upper incomplete gamma function $\Gamma$ is defined by $$\Gamma(s,x)=\displaystyle\int_x^{\infty} t^{s-1}e^{-t} dt.$$
Properties
Theorem
The following formula holds: $$E_n(z)=z^{n-1}\Gamma(1-n,z),$$ where $E_n$ denotes the exponential integral E and $\Gamma$ denotes the incomplete gamma function.
