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 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. 9
 2200380, 8801520, 14913024, 35206080, 140896000, 459818240, 775898880, 2253189120, 16785793024, 22648550400, 36051025920, 51001180160, 144204103680 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS See also the Cohen-te Riele links under A019276. No others < 5*10^11. - Jud McCranie, Feb 08 2012 a(14) > 4*10^12. - Giovanni Resta, Feb 26 2020 6640556211576, 82863343951872, 182140970374656, 480965999895576, 590660008673280, 886341160140800, 5562693163417600, 9386507580211200 are also terms. - Michel Marcus, Feb 27 2020 LINKS Table of n, a(n) for n=1..13. Graeme L. Cohen and Herman J. J. te Riele, Iterating the sum-of-divisors function, Experimental Mathematics, 5 (1996), pp. 93-100. PROG (PARI) isok(n) = sigma(sigma(n))/n == 12; \\ Michel Marcus, Feb 27 2020 CROSSREFS Cf. A019278, A019279, A019281, A019282, A019283, A019284, A019285, A019286, A019287, A019288, A019290, A019291. Sequence in context: A224588 A234332 A251342 * A254803 A254810 A253819 Adjacent sequences: A019286 A019287 A019288 * A019290 A019291 A019292 KEYWORD nonn,more AUTHOR N. J. A. Sloane EXTENSIONS More terms from Jud McCranie, Nov 13 2001, a(9) Feb 01 2012, a(10)-a(13) on Feb 08 2012 STATUS approved

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Last modified May 19 02:48 EDT 2024. Contains 372666 sequences. (Running on oeis4.)