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 A067719 #22 Jan 26 2023 10:17:23 %S A067719 1,2,3,9,12,21,33,72,93,196,228,252,360,475,850,1458,1725,1752,2100, %T A067719 2241,2584,3007,3404,4347,4743,5544,5720,6555,6600,9909,10512,14175, %U A067719 15507,16680,19404,26460,29008,29484,36003,36400,37107,46728,88209,88641,89424,94770 %N A067719 Numbers k such that sigma(k^2 + 1) == 0 (mod k). %H A067719 Amiram Eldar, <a href="/A067719/b067719.txt">Table of n, a(n) for n = 1..250</a> (terms 1..100 from Harvey P. Dale) %p A067719 q:= n-> is(irem(numtheory[sigma](n^2+1), n)=0): %p A067719 select(q, [$1..100000])[]; # _Alois P. Heinz_, Jan 26 2023 %t A067719 Select[Range[50000],Divisible[DivisorSigma[1,#^2+1],#]&] (* _Harvey P. Dale_, Nov 04 2011 *) %Y A067719 Cf. A000203, A002522, A193433. %K A067719 nonn %O A067719 1,2 %A A067719 _Benoit Cloitre_, Feb 05 2002