A217383 - OEIS

%I #21 Apr 23 2025 18:52:23

%S 3,7,11,47,81,95,107,179,233,243,947,2817,2859,3233,7563,11307,218615,

%T 225587,1160027

%N Numbers k such that 8^k - 9 is prime.

%C All terms are equal to 1/3 of the multiples of 3 in A059610.

%C Naturally these numbers are odd since 8^(2n)-9 = (8^n-3)(8^n+3) is composite. - _Bruno Berselli_, Oct 04 2012

%t Select[Range[10000], PrimeQ[8^# - 9] &]

%o (PARI) is(n)=ispseudoprime(8^n-9) \\ _Charles R Greathouse IV_, Jun 13 2017

%Y Cf. A059610, A217356, A217382.

%K nonn,more

%O 1,1

%A _Vincenzo Librandi_, Oct 03 2012

%E a(17)-a(18) using A059610 from _Michael S. Branicky_, Jul 14 2023

%E a(19) using A059610 from _Michael S. Branicky_, Apr 23 2025