1. The problem statement, all variables and given/known data Find the coefficient of x^n in the expansion of ( 1 + x/1! + x^2/2! + x^3/3! + ......... + x^n/n! )^2 . 2. Relevant equations 3. The attempt at a solution At first glance, this looks like the polynomial form of e^x, but the expansion of e^x goes to infinity, so any use of that seems ruled out. Furthermore, I can't try expanding this or writing it in terms of the rth term and equating the power of x to n and doing something with that. Basically, I don't know how to begin.