%I #20 Jul 28 2024 10:58:15

%S 1,2,4,5,6,20,21,22,28,58,120,144,1100,1926,2892,4773,5214,17241,

%T 18980,31265

%N Numbers k such that 12^k + 7 is prime.

%t Do[If[PrimeQ[(12^n+7)],Print[n]],{n,2000}]

%o (PARI) is(n)=ispseudoprime(12^n+7) \\ _Charles R Greathouse IV_, Jun 06 2017

%Y Cf. A137652, A137654.

%K nonn,more

%O 1,2

%A _Zak Seidov_, Feb 01 2008

%E a(15)-a(17) from _Jinyuan Wang_, Mar 03 2020

%E a(18)-a(19) from _Michael S. Branicky_, Mar 15 2023

%E a(20) from _Michael S. Branicky_, Jul 28 2024