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A255682
Numbers k such that 4^k - 2^k - 3 is prime.
0
3, 7, 13, 15, 21, 73, 231, 301, 493, 895, 955, 4069, 5057, 5415, 15325, 19845, 21603, 24577, 37877, 40193, 44283
OFFSET
1,1
COMMENTS
a(22) > 150000. - Hans Havermann, Jul 18 2015
EXAMPLE
3 is in this sequence because 4^3 - 2^3 - 3 = 53.
MATHEMATICA
Select[Range[15000], PrimeQ[4^# - 2^# - 3] &]
PROG
(Magma) [n: n in [1..800] | IsPrime(4^n-2^n-3)];
(PARI) for(n=1, 500, if(ispseudoprime(4^n-2^n-3), print1(n, ", "))) \\ Derek Orr, Mar 03 2015
CROSSREFS
Cf. A098845.
Sequence in context: A209839 A192854 A002236 * A080565 A164344 A002254
KEYWORD
nonn,more
AUTHOR
Vincenzo Librandi, Mar 02 2015
EXTENSIONS
a(15)-a(21) from Hans Havermann, Jul 18 2015
STATUS
approved