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 A253772 Numbers n such that 4^n + 13 is prime. 7
 1, 2, 4, 10, 19, 32, 40, 146, 566, 2054, 9967, 62639, 87814, 141092 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS 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 LINKS MATHEMATICA Select[Range, PrimeQ[4^# + 13] &] PROG (MAGMA) [n: n in [0..2000] | IsPrime(4^n+13)]; (PARI) is(n)=ispseudoprime(4^n+13) \\ Charles R Greathouse IV, Feb 17 2017 CROSSREFS Cf. A104067. 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). Sequence in context: A257593 A197926 A228705 * A043330 A295961 A219555 Adjacent sequences:  A253769 A253770 A253771 * A253773 A253774 A253775 KEYWORD nonn,more AUTHOR Vincenzo Librandi, Jan 12 2015 EXTENSIONS a(11)-a(14) derived from A102634 by Robert Price, Sep 06 2015 STATUS approved

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Last modified January 26 11:20 EST 2020. Contains 331279 sequences. (Running on oeis4.)