> sum('k^4','k=1..n');factor(%);

1/5*(n+1)^5-1/2*(n+1)^4+1/3*(n+1)^3-1/30*n-1/30

1/30*n*(2*n+1)*(n+1)*(3*n^2+3*n-1)

> simplify(%-(1/30)*(n*(n+1)*(2*n+1)*(3*n^2+3*n-1)));

0

>