OFFSET
1,2
COMMENTS
Includes all powers of 5. If a term such as 1555 = 5*311 occurs, so does any number of the form 5^a * 311^b for a>3.
From Alexander Adamchuk, May 16 2010: (Start)
All terms that are not powers of 5 are divisible by 5 and 311.
Prime divisors of a(n) are {5, 311, 6221, 15551, 155501, ...}. (End)
MATHEMATICA
Select[ Range[ 5*10^7], PowerMod[6, #, # ] == 1 & ]
PROG
(PARI) is(n)=Mod(6, n)^n==1 \\ Charles R Greathouse IV, Nov 04 2016
CROSSREFS
KEYWORD
nonn
AUTHOR
EXTENSIONS
Better description from Benoit Cloitre, Mar 06 2002
Edited and extended by Robert G. Wilson v, Jun 18 2002
a(25)-a(45) from Alexander Adamchuk, May 16 2010
STATUS
approved