A262345 Numbers k such that 4^k + 21 is prime.

2, 4, 8, 22, 24, 26, 98, 228, 246, 808, 1556, 1792, 1978, 3424, 69738, 108376, 169584

Offset: 1

Author

Robert Price, Sep 18 2015

Keywords

• nonn
• more

Comments

Half of even terms of A057201. - Elmo R. Oliveira, Nov 29 2023

Examples

			For k = 26, 4^26 + 21 = 4503599627370517 is prime.
		

Crossrefs

Cf. A057201, A156983, A253772.

Programs

Magma

[n: n in [0..700] | IsPrime(4^n+21)];

Mathematica

Select[Range[3000], PrimeQ[4^# + 21] &]

PARI

for(n=1, 1e3, if(isprime(4^n+21), print1(n", "))) \\ Altug Alkan, Sep 18 2015