OFFSET
1,1
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..10000
MATHEMATICA
Select[Range[1000], Mod[2^(# - 1), #] == Length[Divisors[#]] &]
Select[Range[1000], PowerMod[2, #-1, #]==Length[Divisors[#]]&] (* Harvey P. Dale, Nov 19 2015 *)
Select[Range[1000], PowerMod[2, #-1, #] == DivisorSigma[0, #] &] (* Amiram Eldar, Jul 12 2022 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Juri-Stepan Gerasimov, Dec 08 2010
STATUS
approved