# How to find back from generating function $\sum(Q(x)*z^m/m!)$ to $Q(x)$?

How to find back from generating function $\sum_{m=0}^{\infty}(Q(x)\frac{z^m}{m!})$ to $Q$?

In other words, find $Q$ from $\sum_{m=0}^{\infty}(Q(x)\frac{z^m}{m!})$.

finally is generating function depends on $x$ and $z$

Update The reason for this backward action, is forward action from dsolve differential equation solved as special function such as kummer, even convert to ratpoly also can not be success

for example

$\sum_{m=0}^{\infty}(Q(x)\frac{z^m}{m!})$ = 2/(Pi*(exp(x/z)+exp(-x/z)))