Sum

Sum[f, {i, imax}] evaluates the sum from i=1 to imax.

Sum[f, {i, imin, imax}] starts with i=imin.

Sum[f, {i, imin, imax, di}] uses steps di.

Examples

Sum of integers:

Sum[i, {i, 1, 10}]
(* 55 *)

Sum of squares:

Sum[i^2, {i, 1, 5}]
(* 55 *)

Symbolic sum:

Sum[i, {i, 1, n}]
(* n(n+1)/2 *)

Please visit the official Wolfram Language Reference for more details.