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A181476
Numbers k such that k^k == 1 (mod sigma(k)).
0
1, 2, 8, 9, 36, 128, 576, 625, 900, 1156, 2304, 2601, 5185, 6561, 10082, 10404, 27225, 32768, 57600, 117649, 181476, 260100, 285156, 367236, 378225, 443521, 607825, 617796, 645248, 656100, 665856, 783225, 1115136, 1394450, 1500625, 1782225
OFFSET
1,2
COMMENTS
If p is prime then p^m is in the sequence iff m is of the form p^t-1 where t is a nonnegative integer.
MATHEMATICA
Join[{1}, Select[Range[1800000], PowerMod[ #, #, DivisorSigma[1, # ]]==1 &]]
PROG
(PARI) isok(k) = Mod(k, sigma(k))^k == 1; \\ Michel Marcus, Feb 09 2021
CROSSREFS
Sequence in context: A369649 A181887 A221049 * A055678 A301281 A091793
KEYWORD
nonn
AUTHOR
Farideh Firoozbakht, May 23 2010
STATUS
approved