A217350 Numbers k such that 4^k + 9 is prime.

1, 3, 5, 9, 15, 33, 41, 335, 443, 671, 1197, 1355, 2247, 2639, 117293, 191099

Offset: 1

Author

Vincenzo Librandi, Oct 01 2012

Keywords

• nonn
• more

Comments

The next terms are > 250000. - Robert Price, Oct 05 2015

Contains exactly the halved even terms of A057196.

Examples

			For k = 15, 4^15 + 9 = 1073741833 is prime.
		

Crossrefs

Cf. A057196, A089437 (similar sequence).

Programs

Magma

[n: n in [0..700] | IsPrime(4^n+9)]; // Vincenzo Librandi, Oct 06 2015

Mathematica

Select[Range[0, 5000], PrimeQ[4^# + 9] &]

PARI

is(n)=ispseudoprime(4^n+9) \\ Charles R Greathouse IV, Jun 06 2017

Extensions

a(15)-a(16) derived from A057196 by Robert Price, Oct 05 2015