TruncateSum

TruncateSum[sexpr,n] truncates each Sum in sexpr to have at most n terms.

TruncateSum[sexpr,{m,n,…}] truncates each multiple Sum in sexpr using the iterative specification {m,n,…}.

Examples

Truncate an infinite sum to 5 terms:

TruncateSum[Sum[1/n^2, {n, 1, Infinity}], 5]
(* Sum[1/n^2, {n, 1, 5}] *)

Please visit the official Wolfram Language Reference for more details.