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 A113546 #40 Feb 16 2025 08:32:59 %S A113546 120,672,7680,8184,523776,1100190,1124352,14913024,16149760,459818240, %T A113546 775898880,874897408,1476304896,51001180160 %N A113546 Let S(n)=sigma(n)/3. Numbers k such that S(S(k))=k, 1/3-sociable number of order 1 or 2. %C A113546 a(1), a(2), a(5) and a(10) are 3-perfect numbers (A005820). [Corrected by _Mauro Fiorentini_, Jul 21 2015] %C A113546 a(4) = S(a(3)). %C A113546 a(15) > 1.5*10^11. - _Giovanni Resta_, Jul 21 2015 %H A113546 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/SociableNumbers.html">Sociable Numbers</a> %o A113546 (PARI) isok(n) = (type(s=sigma(n)/3) == "t_INT") && (sigma(s)/3 == n); \\ _Michel Marcus_, Feb 20 2014 %Y A113546 A005820 is a subsequence. %Y A113546 Cf. A113286 (1/4-sociable numbers of order 1 or 2). %K A113546 nonn,more %O A113546 1,1 %A A113546 _Yasutoshi Kohmoto_, Jan 27 2006 %E A113546 a(6)-a(9) from _Michel Marcus_, Feb 20 2014 %E A113546 a(10)-a(12) from _Michel Marcus_, Feb 24 2014 %E A113546 a(13)-a(14) from _Giovanni Resta_, Jul 22 2015