OFFSET
1,2
LINKS
Vincenzo Librandi, Table of n, a(n) for n = 1..1000
MATHEMATICA
Select[Range[0, 100], !PrimeQ[2*3^# - 1] &] (* Vincenzo Librandi, Oct 15 2012 *)
PROG
(Magma) [ n: n in [0..100] | not IsPrime(2*3^n-1) ];
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
STATUS
approved