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.

2200380, 8801520, 14913024, 35206080, 140896000, 459818240, 775898880, 2253189120, 16785793024, 22648550400, 36051025920, 51001180160, 144204103680

Offset: 1

Author

N. J. A. Sloane

Keywords

• nonn
• more

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

• Graeme L. Cohen and Herman J. J. te Riele, Iterating the sum-of-divisors function, Experimental Mathematics, 5 (1996), pp. 93-100.

Crossrefs

Cf. A019278, A019279, A019281, A019282, A019283, A019284, A019285, A019286, A019287, A019288, A019290, A019291.

Programs

PARI

isok(n) = sigma(sigma(n))/n  == 12; \\ Michel Marcus, Feb 27 2020

Extensions

More terms from Jud McCranie, Nov 13 2001, a(9) Feb 01 2012, a(10)-a(13) on Feb 08 2012