Generating function for a sequence

The question is as follows:

It is known that the generating function for the sequence , {1,8,27,64,...} is

[x(x^2 + 4x +1)]/(1-x)^4

Use the result to show summation from r=1 to n of r^3 = [n^2(n^2+1)]/4

I know i have to find the sequence represented by 1,8,27,64, .. and once i get the sequence i have to manipulate it until i reach r^3 which will be given by the expression.

My problem is that i cannot find the sequence for 1,8,27,64,...

any help please???

Thank buches!