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
KEYWORD
nonn
AUTHOR
Farideh Firoozbakht, May 23 2010
STATUS
approved