A262971 Numbers k such that 4^k + 31 is prime.

2, 6, 18, 270, 422, 596, 6068, 42140, 64178, 158732, 1509278

Offset

1,1

Comments

The next terms are > 1.5*10^6.

Contains exactly the halved even terms of A247952.

Links

Table of n, a(n) for n=1..11.

Formula

a(n) = A247952(n)/2. - Elmo R. Oliveira, Nov 28 2023

Example

For k = 18, 4^18 + 31 = 68719476767 is prime.

Mathematica

Select[Range[0, 250000], PrimeQ[4^# + 31] &]

Prog

(Magma) [n: n in [0..700] | IsPrime(4^n+31)]; // Vincenzo Librandi, Oct 06 2015
(PARI) for(n=1, 1e3, if(isprime(4^n+31), print1(n", "))) \\ Altug Alkan, Oct 06 2015

Crossrefs

Cf. A247952, A253772 (similar sequence).

Sequence in context: A056743 A064535 A240643 * A253380 A128123 A227884

Adjacent sequences: A262968 A262969 A262970 * A262972 A262973 A262974

Keyword

nonn,more

Author

Robert Price, Oct 05 2015

Extensions

a(11) derived from A247952 by Elmo R. Oliveira, Nov 28 2023

Status

approved