1. The problem statement, all variables and given/known data [sum of; n=1; to infinity] ((2y)^n)/(n(n!)) 2. Relevant equations 3. The attempt at a solution If there were a way to find the improper integral of f(x) = ((2c)^x)/(x(x!)) from one to infinity using unit step integration (c is just a constant), then that would equal the sum, right? Well, I don't know how to do unit step integration, besides by tedious Riemann sums, but I can't do those to infinity. So, an explanation on unit step integration, or some other method of finding the sum of this series, is what I've been looking for for a while now. Thanks.