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 A019286 #41 Dec 27 2021 21:09:39 %S A019286 168,10752,331520,691200,1556480,1612800,106151936,5099962368, %T A019286 4010593484800 %N A019286 Let sigma_m (n) be result of applying sum-of-divisors function m times to n; call n (m,k)-perfect if sigma_m (n) = k*n; sequence gives the (2,9)-perfect numbers. %C A019286 See also the Cohen-te Riele links under A019276. %C A019286 No other terms < 5*10^11. - _Jud McCranie_, Feb 08 2012 %C A019286 4010593484800 is also a term. See comment in A019278. - _Michel Marcus_, May 15 2016 %H A019286 Graeme L. Cohen and Herman J. J. te Riele, <a href="http://projecteuclid.org/euclid.em/1047565640">Iterating the sum-of-divisors function</a>, Experimental Mathematics, 5 (1996), pp. 93-100. %o A019286 (PARI) isok(n) = sigma(sigma(n))/n == 9; \\ _Michel Marcus_, May 12 2016 %Y A019286 Cf. A000668, A019278, A019279, A019281, A019282, A019283, A019284, A019285, A019286, A019287, A019288, A019289, A019290, A019291. %K A019286 nonn,more %O A019286 1,1 %A A019286 _N. J. A. Sloane_ %E A019286 a(8) by _Jud McCranie_, Jan 28 2012 %E A019286 a(9) from _Giovanni Resta_, Feb 26 2020