A216889 Numbers k such that 12*3^k + 1 is prime.

0, 1, 2, 5, 13, 14, 38, 200, 248, 884, 1004, 1253, 1634, 3305, 3521, 9601, 19784, 72697

Offset: 1

Author

Vincenzo Librandi, Sep 26 2012

Keywords

• nonn
• more

Comments

a(19) > 2*10^5. - Robert Price, Mar 16 2014

All terms are verified primes (i.e., not merely probable primes). - Robert Price, Mar 16 2014

Crossrefs

Cf. A003306, A005537-A005539, A056805.

Programs

Magma

[n: n in [0..4000] | IsPrime(12*3^n + 1)];

Mathematica

Select[Range[4000], PrimeQ[12 * 3^# + 1] &]

PARI

is(n)=ispseudoprime(12*3^n+1) \\ Charles R Greathouse IV, Jun 13 2017

Formula

a(n) = A005537(n+1) - 1. - Bruno Berselli, Sep 27 2012

Extensions

a(16)-a(17) from Vincenzo Librandi, Sep 30 2012

a(18) from Robert Price, Mar 16 2014