A177103 Numbers n >= 0 such that 2*3^n - 1 is not prime.

0, 4, 5, 6, 9, 10, 11, 13, 14, 15, 16, 17, 18, 19, 21, 22, 24, 25, 26, 28, 29, 30, 31, 32, 33, 34, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 57, 58, 59, 60, 61, 63, 64, 65, 66, 67, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84

Offset: 1

Author

Vincenzo Librandi

Keywords

• nonn
• easy

Links

• Vincenzo Librandi, Table of n, a(n) for n = 1..1000

Crossrefs

Cf. A003307 (Numbers n such that 2*3^n-1 is prime).

Programs

Magma

[ n: n in [0..100] | not IsPrime(2*3^n-1) ];

Mathematica

Select[Range[0, 100], !PrimeQ[2*3^# - 1] &] (* Vincenzo Librandi, Oct 15 2012 *)