A019290 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 (2,13)-perfect numbers.

57120, 932064, 3932040, 251650560

Offset: 1

Author

N. J. A. Sloane

Keywords

• nonn
• more

Comments

See also the Cohen-te Riele links under A019276.

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

11383810648416 is also a term. See comment in A019278. - Michel Marcus, May 15 2016

a(5) > 4*10^12. - Giovanni Resta, Feb 26 2020

50248050278400, 117245450649600, 86575337046016000 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. A019276, A019278, A019279, A019281, A019282, A019283, A019284, A019285, A019286, A019287, A019288, A019289, A019291.

Programs

PARI

isok(n) = sigma(sigma(n))/n == 13; \\ Michel Marcus, May 15 2016