A074385 Square root of sum of divisors, when it is a square.

1, 2, 6, 12, 12, 11, 12, 12, 12, 18, 24, 18, 16, 18, 24, 24, 24, 20, 24, 24, 28, 24, 24, 31, 30, 24, 36, 24, 24, 36, 32, 28, 36, 36, 30, 36, 36, 42, 36, 42, 32, 48, 36, 48, 42, 42, 40, 42, 60, 56, 48, 48, 42, 36, 62, 36, 36, 48, 40, 60, 48, 42, 48, 40, 48, 60, 48, 56, 60, 48

Offset: 1

Author

Labos Elemer, Aug 22 2002

Keywords

• nonn
• look

Links

• Ivan Neretin, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A000203, A006532.

Programs

Mathematica

Select[Sqrt[DivisorSigma[1, Range@1800]], IntegerQ] (* Ivan Neretin, Jun 05 2015 *)

PARI

lista(nn) = {for (n=1, nn, if (issquare(s=sigma(n)), print1(sqrtint(s), ", ")););} \\ Michel Marcus, Dec 18 2013

Formula

a(n) = sqrt(A000203(A006532(n))).