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A019278
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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 (2,k)-perfect numbers.
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4
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1, 2, 4, 8, 15, 16, 21, 24, 42, 60, 64, 84, 160, 168, 240, 336, 480, 504, 512, 960, 1023, 1344, 1536, 4092, 4096, 10752, 13824, 16368, 29127, 32256, 32736, 47360, 57120, 58254, 61440, 65472, 65536, 86016, 116508, 217728, 262144, 331520
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,2
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COMMENTS
| See also the Cohen-te Reile links under A019276.
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REFERENCES
| Graeme L. Cohen and Herman J. J. te Riele, Iterating the sum-of-divisors function, Experimental Mathematics, 5 (1996), pp. 93-100.
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LINKS
| Jud McCranie, Table of n, a(n) for n = 1..130
Experimental Mathematics, Home Page
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MATHEMATICA
| Select[Range[100000], Mod[DivisorSigma[1, DivisorSigma[1, #]], #] == 0 &] (* Carl Najafi, Aug 22 2011 *)
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CROSSREFS
| Cf. A098219-A098223, A008333, A051027.
Sequence in context: A098056 A097100 A002954 * A084345 A084561 A078613
Adjacent sequences: A019275 A019276 A019277 * A019279 A019280 A019281
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KEYWORD
| nonn,changed
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AUTHOR
| N. J. A. Sloane (njas(AT)research.att.com).
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