I was trying to evaluate the following integral using sage
integrate(x*x/(exp(x)+1),x,0,oo)
and I get the following answer
3/2*zeta(3) + limit(1/3*x^3 - x^2*log(e^x + 1) - 2*x*polylog(2, -e^x) +
2*polylog(3, -e^x), x, +Infinity, minus)
However, mathematica gives just the first term 3/2*zeta(3). Is there a way to get just the zeta function for integrals of the form x^n/(exp(x)+1)? The limit makes it difficult to calculate the numerical values in the end
