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