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 A019284 #45 Feb 27 2020 04:34:30 %S A019284 24,1536,47360,343976,572941926400 %N A019284 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 (2,7)-perfect numbers. %C A019284 See also the Cohen-te Riele links under A019276. %C A019284 No other terms < 5*10^11. - _Jud McCranie_, Feb 08 2012 %C A019284 572941926400 is also a term. See comment in A019278. - _Michel Marcus_, May 15 2016 %C A019284 a(6) > 4*10^12, if it exists. - _Giovanni Resta_, Feb 26 2020 %H A019284 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. %t A019284 Select[Range[50000], DivisorSigma[1, DivisorSigma[1, #]]/# == 7 &] (* _Robert Price_, Apr 07 2019 *) %o A019284 (PARI) isok(n) = sigma(sigma(n))/n == 7; \\ _Michel Marcus_, May 12 2016 %Y A019284 Cf. A000668, A019278, A019279, A019281, A019282, A019283, A019285, A019286, A019287, A019288, A019289, A019290, A019291. %K A019284 nonn,more %O A019284 1,1 %A A019284 _N. J. A. Sloane_ %E A019284 a(5) from _Giovanni Resta_, Feb 26 2020