Entire exponential integral
From specialfunctionswiki
The $\mathrm{Ein}$ function is defined by $$\mathrm{Ein}(z)=\displaystyle\int_0^z \dfrac{1-e^{-t}}{t} \mathrm{d}t.$$
The $\mathrm{Ein}$ function is defined by $$\mathrm{Ein}(z)=\displaystyle\int_0^z \dfrac{1-e^{-t}}{t} \mathrm{d}t.$$
