A263983 Odd integers k such that sigma(k)^2 is divisible by k.

1, 1521, 5733, 92781, 108927, 544635, 628849, 1886547, 2069613, 2723175, 2876211, 5659641, 16978923, 40847625, 45623655, 50936769, 60998353, 84418425, 84894615, 89162541, 173369889, 182995059, 191166885, 262840851, 401164731, 424473075, 426988471

Offset: 1

Author

Michel Marcus, Oct 31 2015

Keywords

• nonn

Comments

Odd terms of A263928.

Crossrefs

Cf. A000203, A017665, A017666, A263928.

Programs

Mathematica

fQ[n_]:=IntegerQ[DivisorSigma[1,n]^2/n];Select[Range[1,1886547,2],fQ[#]&] (* Ivan N. Ianakiev, Nov 03 2015 *)

PARI

lista(nn) = forstep(n=1, nn, 2, if (denominator(sigma(n)^2/n) == 1, print1(n, ", ")));

Extensions

a(21)-a(27) from Ivan N. Ianakiev, Oct 31 2015