hey, just confirming some other problems

i am asked to find the first 4 terms of ln(1+e^x) in the maclaurin series

so i got
f(x) = ln(1+e^x)
f`x = e^x/1!(1+e^x)
f``x = e^x/2!(1+e^x)^2
but im not too sure i know if this is right so if someone could let me know...
f```x = 2/3!(1+e^x)^3

and i am asked to find the sum of (2^3n - 1)/3^2n for which i got 3.5? im not too sure about that one aswell.