I need to find a formula that will work with any number.

I am finding the volume of a 3d cross- shape. Here are my results so far:

Term Number 0 1 2 3 4 5
nth term 1 7 25 63 129 231
1rst diff 6 18 38 66 102
2nd diff 12 20 28 36
3rd diff 8 8 8

I can't seem to find a formula that will work with any number. Any help would be much appreciated.

Answered by Penny Nom.