A019288 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 (2,11)-perfect numbers.

4404480, 57669920, 238608384

Offset: 1

Author

N. J. A. Sloane

Keywords

• nonn
• bref
• more

Comments

See also the Cohen-te Riele links under A019276.

No other terms < 5*10^11. - Jud McCranie, Feb 08 2012

a(4) > 4*10^12. - Giovanni Resta, Feb 26 2020

53283599155200, 2914255525994496 and 3887055949004800 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, A019289, A019290, A019291.

Programs

PARI

isok(n) = sigma(sigma(n))/n  == 11; \\ Michel Marcus, Feb 27 2020