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 A146747 #8 Apr 07 2024 09:10:01
%S A146747 2,3,5,6,7,20,30
%N A146747 Numbers k such that sigma_1(k)*sigma_0(k)/(sigma_1(k)-sigma_0(k)) is an integer.
%C A146747 Numbers k such that A000203(k)*A000005(k)/(A000203(k)-A000005(k)) is an integer.
%t A146747 q[n_] := Module[{s = DivisorSigma[1, n], d = DivisorSigma[0, n]}, Divisible[s*d, s - d]]; Select[Range[2, 100], q] (* _Amiram Eldar_, Apr 07 2024 *)
%o A146747 (PARI) is(n) = {my(f = factor(n), s = sigma(f), d = numdiv(f)); n > 1 && !((s*d) % (s-d));} \\ _Amiram Eldar_, Apr 07 2024
%Y A146747 Cf. A000005, A000203, A063647, A083795.
%K A146747 nonn,more
%O A146747 1,1
%A A146747 _Ctibor O. Zizka_, Nov 01 2008