DivisorSum

DivisorSum[n,form] represents the sum of form[i] for all i that divide n.

DivisorSum[n,form,cond] includes only those divisors for which cond[i] gives True.

Examples

Sum the squares of divisors:

DivisorSum[12, #^2 &]
(* 210 *)

Sum only odd divisors:

DivisorSum[12, # &, OddQ]
(* 4 *)

Please visit the official Wolfram Language Reference for more details.