This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A263983 #29 Mar 11 2024 01:45:18 %S A263983 1,1521,5733,92781,108927,544635,628849,1886547,2069613,2723175, %T A263983 2876211,5659641,16978923,40847625,45623655,50936769,60998353, %U A263983 84418425,84894615,89162541,173369889,182995059,191166885,262840851,401164731,424473075,426988471 %N A263983 Odd integers k such that sigma(k)^2 is divisible by k. %C A263983 Odd terms of A263928. %t A263983 fQ[n_]:=IntegerQ[DivisorSigma[1,n]^2/n];Select[Range[1,1886547,2],fQ[#]&] (* _Ivan N. Ianakiev_, Nov 03 2015 *) %o A263983 (PARI) lista(nn) = forstep(n=1, nn, 2, if (denominator(sigma(n)^2/n) == 1, print1(n, ", "))); %Y A263983 Cf. A000203, A017665, A017666, A263928. %K A263983 nonn %O A263983 1,2 %A A263983 _Michel Marcus_, Oct 31 2015 %E A263983 a(21)-a(27) from _Ivan N. Ianakiev_, Oct 31 2015