A262969 Numbers k such that 4^k + 27 is prime.

1, 2, 4, 5, 7, 8, 20, 22, 43, 55, 67, 77, 92, 97, 154, 160, 533, 748, 1432, 3143, 6427, 8257, 8270, 9623, 12269, 28822, 32683, 42638, 97427, 133340, 188395, 239044

Offset: 1

Author

Robert Price, Oct 05 2015

Keywords

• nonn
• more

Comments

The next terms are > 239044.

Contains exactly the halved even terms of A157007.

Examples

			For k = 22, 4^22 + 27 = 17592186044443 is prime.
		

Crossrefs

Cf. A157007, A253772 (similar sequence).

Programs

Magma

[n: n in [0..700] | IsPrime(4^n+27)]; // Vincenzo Librandi, Oct 06 2015

Mathematica

Select[Range[0, 250000], PrimeQ[4^# + 27] &]

PARI

for(n=1, 1e3, if(isprime(4^n+3^3), print1(n", "))) \\ Altug Alkan, Oct 06 2015

Extensions

a(32) derived from A157007 by Elmo R. Oliveira, Nov 28 2023