A closed form for the sum is 1 - (a^n+b)/(3^2n+c - 1) where a and b are integers. Find

A closed form for the sum \(S = \frac {2}{3+1} + \frac {2^2}{3^2+1} + \cdots + \frac {2^{n+1}}{3^{2^n}+1}\)
is  1 - (a^n+b)/(3^2n+c - 1) where a and b are integers. Find a+ b+ c