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 A019289 #38 Sep 29 2023 22:04:04 %S A019289 2200380,8801520,14913024,35206080,140896000,459818240,775898880, %T A019289 2253189120,16785793024,22648550400,36051025920,51001180160, %U A019289 144204103680 %N A019289 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 (2,12)-perfect numbers. %C A019289 See also the Cohen-te Riele links under A019276. %C A019289 No others < 5*10^11. - _Jud McCranie_, Feb 08 2012 %C A019289 a(14) > 4*10^12. - _Giovanni Resta_, Feb 26 2020 %C A019289 6640556211576, 82863343951872, 182140970374656, 480965999895576, 590660008673280, 886341160140800, 5562693163417600, 9386507580211200 are also terms. - _Michel Marcus_, Feb 27 2020 %H A019289 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 A019289 (PARI) isok(n) = sigma(sigma(n))/n == 12; \\ _Michel Marcus_, Feb 27 2020 %Y A019289 Cf. A019278, A019279, A019281, A019282, A019283, A019284, A019285, A019286, A019287, A019288, A019290, A019291. %K A019289 nonn,more %O A019289 1,1 %A A019289 _N. J. A. Sloane_ %E A019289 More terms from _Jud McCranie_, Nov 13 2001, a(9) Feb 01 2012, a(10)-a(13) on Feb 08 2012