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 A206421 #21 Dec 16 2024 02:02:32 %S A206421 12,18,12,24,24,31,18,42,32,24,60,31,42,56,72,32,48,54,48,60,56,90,42, %T A206421 96,84,72,48,124,72,98,54,120,72,120,80,90,60,168,96,104,84,144,126, %U A206421 96,144,72,114,124,140,96,168,80,186,126,84,224,108,132,120,180 %N A206421 Corresponding values of sigma(m) of numbers in A206036. %H A206421 Amiram Eldar, <a href="/A206421/b206421.txt">Table of n, a(n) for n = 1..10000</a> %H A206421 Max Alekseyev, <a href="https://oeis.org/wiki/User:Max_Alekseyev/gpscripts">PARI/GP Scripts for Miscellaneous Math Problems</a> (invphi.gp). %F A206421 a(n) = A000203(A206036(n)). - _Amiram Eldar_, Dec 15 2024 %e A206421 a(1) = 12 because sigma(A206036(1)) = sigma(6) = 12. %o A206421 (PARI) list(lim) = my(s); for(k = 1, lim, s = sigma(k); if(invsigmaNum(s) > 1, print1(s, ", "))); \\ _Amiram Eldar_, Dec 15 2024, using _Max Alekseyev_'s invphi.gp %Y A206421 Cf. A000203, A159886 (values k such that sigma(x)= k has more than one solution), A206036 (numbers m such that sigma(m) = sigma(k) has solution for distinct k). %K A206421 nonn %O A206421 1,1 %A A206421 _Jaroslav Krizek_, Feb 07 2012