

A019286


Let sigma_m (n) be result of applying sumofdivisors function m times to n; call n (m,k)perfect if sigma_m (n) = k*n; sequence gives the (2,9)perfect numbers.


2




OFFSET

1,1


COMMENTS

See also the Cohente Riele links under A019276.
No other terms < 5*10^11.  Jud McCranie, Feb 08 2012
4010593484800 is also a term. See comment in A019278.  Michel Marcus, May 15 2016


LINKS

Table of n, a(n) for n=1..8.
Graeme L. Cohen and Herman J. J. te Riele, Iterating the sumofdivisors function, Experimental Mathematics, 5 (1996), pp. 93100.


PROG

(PARI) isok(n) = sigma(sigma(n))/n == 9; \\ Michel Marcus, May 12 2016


CROSSREFS

Cf. A000668, A019278, A019279, A019282, A019283, A019284.
Sequence in context: A278010 A006363 A271033 * A218413 A064767 A115222
Adjacent sequences: A019283 A019284 A019285 * A019287 A019288 A019289


KEYWORD

nonn,more


AUTHOR

N. J. A. Sloane.


EXTENSIONS

a(8) by Jud McCranie, Jan 28 2012


STATUS

approved



