

A262345


Numbers n such that 4^n + 21 is prime.


1



2, 4, 8, 22, 24, 26, 98, 228, 246, 808, 1556, 1792, 1978, 3424, 69738, 108376, 169584
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OFFSET

1,1


LINKS

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


FORMULA

a(n) = half of even terms of A057201.


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. similar sequences listed in A253772.
Cf. A057201.
Sequence in context: A055876 A065847 A133604 * A192149 A115778 A295628
Adjacent sequences: A262342 A262343 A262344 * A262346 A262347 A262348


KEYWORD

nonn,more


AUTHOR

Robert Price, Sep 18 2015


STATUS

approved



