A253774 Numbers k such that 4^k + 19 is prime.

1, 3, 15, 81, 327, 357, 685, 831, 861, 1405, 38571, 78127, 216487, 546121, 622615

Offset

1,2

Links

Table of n, a(n) for n=1..15.

Formula

a(n) = A057221(n)/2. - Joerg Arndt, Aug 28 2015

Example

15 is a term because 4^15 + 19 = 1073741843 is prime.

Mathematica

Select[Range[3000], PrimeQ[4^# + 19] &]

Prog

(Magma) [n: n in [0..700] | IsPrime(4^n+19)];
(PARI) is(n)=ispseudoprime(4^n+19) \\ Charles R Greathouse IV, Jun 06 2017

Crossrefs

Cf. A057221, A104068, A253772 (similar sequence).

Sequence in context: A369085 A020044 A024338 * A003448 A229841 A198628

Adjacent sequences: A253771 A253772 A253773 * A253775 A253776 A253777

Keyword

nonn,more

Author

Vincenzo Librandi, Jan 16 2015

Extensions

Three more term (using A057221) from Joerg Arndt, Aug 28 2015

a(14)-a(15) derived from A057221 by Elmo R. Oliveira, Nov 28 2023

Status

approved