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A070286
Numbers k such that the equation sigma(sigma(x)) = k 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
OFFSET
1,2
COMMENTS
Complement of A162923. - Jaroslav Krizek, Jul 19 2009
LINKS
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
KEYWORD
easy,nonn
AUTHOR
Benoit Cloitre, May 10 2002
STATUS
approved