A253773 Numbers k such that 4^k + 15 is prime.

1, 2, 3, 4, 5, 6, 8, 11, 13, 15, 16, 20, 21, 23, 36, 38, 90, 99, 155, 164, 171, 254, 255, 273, 404, 1386, 1941, 1970, 2420, 3759, 5559, 5776, 6369, 6429, 22061, 32330, 81780, 90248, 162933, 240920, 504584

Offset: 1

Author

Vincenzo Librandi, Jan 12 2015

Keywords

• nonn
• more

Comments

Half of even terms of A057197. - Michel Marcus, Aug 28 2015

Examples

			For k = 15, 4^15 + 15 = 1073741839 is prime.
		

Crossrefs

Cf. A057197, A237418, A253772 (similar sequence).

Programs

Magma

[n: n in [0..1300] | IsPrime(4^n+15)];

Mathematica

Select[Range[10000], PrimeQ[4^# + 15] &]

PARI

is(n)=isprime(4^n + 15) \\ Anders Hellström, Aug 28 2015

Extensions

a(31)-a(39) from A057197 data by Michel Marcus, Aug 28 2015

a(40) derived from A057197 by Robert Price, Sep 18 2015

a(41) from A057197 data by Elmo R. Oliveira, Dec 11 2023