Suma de potencias

S(n,1)=n(n+1)/2
S(n,2)=n(n+1)(2n+1)/6
S(n,3)=n^2(n+1)^2/4
S(n,4)=n(n+1)(6n^3+9n^2+n-1)/30
S(n,5)=n^2(n+1)^2(2n^2+2n-1)/12