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A070286 Numbers n such that the equation sigma(sigma(x)) = n has solutions. 3
1, 4, 7, 8, 12, 14, 15, 24, 28, 32, 39, 42, 56, 60, 63, 72, 80, 84, 90, 91, 96, 104, 112, 114, 120, 124, 126, 128, 133, 160, 168, 171, 186, 195, 210, 216, 224, 234, 240, 248, 252, 255, 256, 260, 280, 288, 294, 300, 308, 312, 336, 360, 363, 372, 378, 384, 392 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Complement of A162923. - Jaroslav Krizek, Jul 19 2009

LINKS

Ivan Neretin, Table of n, a(n) for n = 1..10000

MATHEMATICA

mx = 400; Select[Union@Table[Nest[DivisorSigma[1, #] &, n, 2], {n, mx}], # < mx &] (* Ivan Neretin, Feb 12 2018 *)

CROSSREFS

Cf. A162923.

Sequence in context: A189223 A060833 A162967 * A324978 A047536 A093494

Adjacent sequences:  A070283 A070284 A070285 * A070287 A070288 A070289

KEYWORD

easy,nonn

AUTHOR

Benoit Cloitre, May 10 2002

STATUS

approved

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Last modified January 20 10:51 EST 2020. Contains 331081 sequences. (Running on oeis4.)