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A019286 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 (2,9)-perfect numbers. 2
168, 10752, 331520, 691200, 1556480, 1612800, 106151936, 5099962368 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

See also the Cohen-te Reile 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 sum-of-divisors function, Experimental Mathematics, 5 (1996), pp. 93-100.

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: A003800 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

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Last modified May 31 10:28 EDT 2016. Contains 273543 sequences.