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

%I #29 Mar 11 2024 01:45:18

%S 1,1521,5733,92781,108927,544635,628849,1886547,2069613,2723175,

%T 2876211,5659641,16978923,40847625,45623655,50936769,60998353,

%U 84418425,84894615,89162541,173369889,182995059,191166885,262840851,401164731,424473075,426988471

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

%C Odd terms of A263928.

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

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

%Y Cf. A000203, A017665, A017666, A263928.

%K nonn

%O 1,2

%A _Michel Marcus_, Oct 31 2015

%E a(21)-a(27) from _Ivan N. Ianakiev_, Oct 31 2015