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

1,1

Comments

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

Links

Table of n, a(n) for n=1..17.

Example

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

Mathematica

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

Prog

(Magma) [n: n in [0..700] | IsPrime(4^n+21)];
(PARI) for(n=1, 1e3, if(isprime(4^n+21), print1(n", "))) \\ Altug Alkan, Sep 18 2015

Crossrefs

Cf. A057201, A156983, A253772.

Sequence in context: A055876 A065847 A133604 * A192149 A115778 A333016

Adjacent sequences: A262342 A262343 A262344 * A262346 A262347 A262348

Keyword

nonn,more

Author

Robert Price, Sep 18 2015

Status

approved