DivisorSum

DivisorSum(n, head)

returns the sum of the divisors of n. The head is applied to each divisor.

DivisorSum(n, head, condition)

The condition checks, if the divisor should be summed up.

See:

• Wikipedia - Divisor sum identities

Examples

Calculate the OEIS - sequence A002791:

>> a(n_) := DivisorSum(n, #^2 &, # < 5 &) + 4 * DivisorSum(n, # &, # > 4 &); Array(a, 70)
{1,5,10,21,21,38,29,53,46,65,45,102,53,89,90,117,69,146,77,161,122,137,93,230,
121,161,154,217,117,278,125,245,186,209,189,354,149,233,218,353,165,374,173,329,
306,281,189,486,225,365,282,385,213,470,285,473,314,353,237,662,245,377,410,501,
333,566,269,497,378,569}

Implementation status

• ☑ - partially implemented

Github

• Implementation of DivisorSum