A181476 Numbers k such that k^k == 1 (mod sigma(k)).

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.

Links

Table of n, a(n) for n=1..36.

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

Cf. A000203, A177006.

Sequence in context: A369649 A181887 A221049 * A055678 A301281 A091793

Adjacent sequences: A181473 A181474 A181475 * A181477 A181478 A181479

Keyword

nonn

Author

Farideh Firoozbakht, May 23 2010

Status

approved