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A253774
Numbers k such that 4^k + 19 is prime.
2
1, 3, 15, 81, 327, 357, 685, 831, 861, 1405, 38571, 78127, 216487, 546121, 622615
OFFSET
1,2
FORMULA
a(n) = A057221(n)/2. - Joerg Arndt, Aug 28 2015
EXAMPLE
15 is a term because 4^15 + 19 = 1073741843 is prime.
MATHEMATICA
Select[Range[3000], PrimeQ[4^# + 19] &]
PROG
(Magma) [n: n in [0..700] | IsPrime(4^n+19)];
(PARI) is(n)=ispseudoprime(4^n+19) \\ Charles R Greathouse IV, Jun 06 2017
CROSSREFS
Cf. A057221, A104068, A253772 (similar sequence).
Sequence in context: A369085 A020044 A024338 * A003448 A229841 A198628
KEYWORD
nonn,more
AUTHOR
Vincenzo Librandi, Jan 16 2015
EXTENSIONS
Three more term (using A057221) from Joerg Arndt, Aug 28 2015
a(14)-a(15) derived from A057221 by Elmo R. Oliveira, Nov 28 2023
STATUS
approved