A057472 Numbers k such that 2*6^k - 1 is prime.

1, 2, 3, 4, 5, 12, 16, 26, 27, 36, 40, 45, 49, 52, 53, 75, 140, 150, 167, 245, 250, 755, 785, 825, 970, 1235, 1289, 1477, 1739, 1872, 1976, 1993, 2175, 4218, 7656, 10898, 13410, 13625, 15706, 33003, 44288, 45556, 48855, 60522, 62795, 98898, 118429, 153714

Offset: 1

Author

Robert G. Wilson v, Sep 10 2000

Keywords

• nonn

Comments

a(49) > 2*10^5. - Robert Price, Jan 06 2016 [Since a(39) was missing before, this a(49) should actually be a(50). - Jianing Song, Sep 22 2018]

Numbers k such that A164559(k+1) is prime.

Crossrefs

Cf. A164559.

Programs

Magma

[n: n in [0..2000] |IsPrime(2*6^n - 1)]; // Vincenzo Librandi, Sep 23 2018

Mathematica

Select[Range[1000], PrimeQ[2*6^# - 1] &] (* Giovanni Resta, May 19 2016 *)

PARI

is(n)=ispseudoprime(2*6^n-1) \\ Charles R Greathouse IV, Feb 17 2017

Extensions

More terms from Pierre CAMI, Jun 16 2006

Edited by Michel Marcus, Jan 06 2012

a(41)-a(48) from Robert Price, Jan 06 2016

Missing a(39) from Pierre CAMI, May 19 2016