Voozh

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

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,2

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.

LINKS

Table of n, a(n) for n=1..48.

MATHEMATICA

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

PROG

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