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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 (list; graph; refs; listen; history; text; internal format)
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

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Last modified November 21 03:20 EST 2018. Contains 317427 sequences. (Running on oeis4.)