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A217350
Numbers k such that 4^k + 9 is prime.
2
1, 3, 5, 9, 15, 33, 41, 335, 443, 671, 1197, 1355, 2247, 2639, 117293, 191099
OFFSET
1,2
COMMENTS
The next terms are > 250000. - Robert Price, Oct 05 2015
Contains exactly the halved even terms of A057196.
EXAMPLE
For k = 15, 4^15 + 9 = 1073741833 is prime.
MATHEMATICA
Select[Range[0, 5000], PrimeQ[4^# + 9] &]
PROG
(Magma) [n: n in [0..700] | IsPrime(4^n+9)]; // Vincenzo Librandi, Oct 06 2015
(PARI) is(n)=ispseudoprime(4^n+9) \\ Charles R Greathouse IV, Jun 06 2017
CROSSREFS
Cf. A057196, A089437 (similar sequence).
Sequence in context: A140428 A340849 A027154 * A210844 A200148 A052007
KEYWORD
nonn,more
AUTHOR
Vincenzo Librandi, Oct 01 2012
EXTENSIONS
a(15)-a(16) derived from A057196 by Robert Price, Oct 05 2015
STATUS
approved