A262971 Numbers k such that 4^k + 31 is prime.

2, 6, 18, 270, 422, 596, 6068, 42140, 64178, 158732, 1509278

Offset: 1

Author

Robert Price, Oct 05 2015

Keywords

• nonn
• more

Comments

The next terms are > 1.5*10^6.

Contains exactly the halved even terms of A247952.

Examples

			For k = 18, 4^18 + 31 = 68719476767 is prime.
		

Crossrefs

Cf. A247952, A253772 (similar sequence).

Programs

Magma

[n: n in [0..700] | IsPrime(4^n+31)]; // Vincenzo Librandi, Oct 06 2015

Mathematica

Select[Range[0, 250000], PrimeQ[4^# + 31] &]

PARI

for(n=1, 1e3, if(isprime(4^n+31), print1(n", "))) \\ Altug Alkan, Oct 06 2015

Formula

a(n) = A247952(n)/2. - Elmo R. Oliveira, Nov 28 2023

Extensions

a(11) derived from A247952 by Elmo R. Oliveira, Nov 28 2023