OFFSET
1,2
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..10000
MATHEMATICA
Select[Range[8000], !PrimeQ[#] && PowerMod[10, #, #] == Mod[10, #] && !(# > 1 && Divisible[# - 1, CarmichaelLambda[#]]) &] (* Amiram Eldar, Mar 19 2020 *)
PROG
(PARI) isok(n) = !isprime(n) && !is_A002997(n) && (Mod(10^n, n) == Mod(10, n)); \\ Michel Marcus, Nov 06 2013
CROSSREFS
KEYWORD
nonn
AUTHOR
Artur Jasinski, Dec 28 2008
EXTENSIONS
New name from Michel Marcus, Nov 06 2013
STATUS
approved