

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
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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



