I'm afraid my math in this area is a bit deficient, but what I am trying to do is see if there's a way to simplify the function: but I never really learned how to manipulate factorials algebraically, ...

In this paper, we firstly introduce the polylogarithms and incomplete gamma function. Then, we claim that there is a relation between polylogarithms and a generalization of incomplete gamma function.

We define the incomplete gamma function ratio for positive N by \begin{align*}\tag{1}P(N, b, X) &= \int^X_0 t^{N-1}e^{-bt} dt/ \int^\infty_0 t^{N-1}e^{-bt} dt ...