# [✓] Increment in multiple sum indices?

GROUPS:
 Hello, I am trying to write nested sums of the following form:But i need the index j to run from 0 with an increment as follows:any suggestions? Thanks
 Gianluca Gorni 2 Votes You can use Fold: With[{k = 2}, Fold[Sum[#1, {Subscript[a, #2], 0, n}] &, Sum[a[i] x^i, {i, 0, n}], Range[0, k]]]