A019291 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 (2,14)-perfect numbers.

217728, 1278720, 2983680, 5621760, 14008320, 298721280, 955367424, 1874780160, 4874428416, 1957928934528

Offset

1,1

Comments

See also the Cohen-te Riele links under A019276.

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

36095341363200 is also a term. See comment in A019278. - Michel Marcus, May 15 2016

a(11) > 4*10^12. - Giovanni Resta, Feb 26 2020

Links

Table of n, a(n) for n=1..10.

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

Prog

(PARI) isok(n) = sigma(sigma(n))/n == 14; \\ Michel Marcus, May 15 2016

Crossrefs

Cf. A019276, A019278, A019279, A019281, A019282, A019283, A019284, A019285, A019286, A019287, A019288, A019289, A019290.

Sequence in context: A077640 A188347 A078520 * A205734 A205915 A205907

Adjacent sequences: A019288 A019289 A019290 * A019292 A019293 A019294

Keyword

nonn

Author

N. J. A. Sloane

Extensions

More terms from Jud McCranie, Nov 13 2001

a(9) from Jud McCranie, Jan 28 2012

a(10) from Giovanni Resta, Feb 26 2020

Status

approved