A019281 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 (2,3)-perfect numbers.

8, 21, 512

Offset

1,1

Comments

See also the Cohen-te Riele links under A019276.

No further term < 10^9 [see Table 1].

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

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

Links

Table of n, a(n) for n=1..3.

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

Experimental Mathematics, Home Page.

Crossrefs

Cf. A019278, A019279, A019282, A019283, A019284, A019285, A019286, A019287, A019288, A019289, A019290, A019291.

Sequence in context: A156239 A141369 A060390 * A284737 A323593 A013630

Adjacent sequences: A019278 A019279 A019280 * A019282 A019283 A019284

Keyword

nonn,bref,more

Author

N. J. A. Sloane

Status

approved