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 A253772 Numbers n such that 4^n + 13 is prime. 7

%I

%S 1,2,4,10,19,32,40,146,566,2054,9967,62639,87814,141092

%N Numbers n such that 4^n + 13 is prime.

%C Numbers of the form 4^n+k (for n>0) are never primes when k is even (obviously) or when k == -1 (mod 6): in the last case, in fact, (3+1)^n + 6*h-1 is divisible by 3. - _Bruno Berselli_, Oct 06 2015

%t Select[Range[4000], PrimeQ[4^# + 13] &]

%o (MAGMA) [n: n in [0..2000] | IsPrime(4^n+13)];

%o (PARI) is(n)=ispseudoprime(4^n+13) \\ _Charles R Greathouse IV_, Feb 17 2017

%Y Cf. A104067.

%Y Cf. numbers n such that 4^n+k is prime: A089437 (k=3), A217349 (k=7), A217350 (k=9), this sequence (k=13), A253773 (k=15), A253774 (k=19), A262345 (k=21), A204388 (k=25), A262969 (k=27), A262971 (k=31), A262972 (k=33).

%K nonn,more

%O 1,2

%A _Vincenzo Librandi_, Jan 12 2015

%E a(11)-a(14) derived from A102634 by _Robert Price_, Sep 06 2015

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Last modified November 16 21:47 EST 2018. Contains 317275 sequences. (Running on oeis4.)