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A138699
Numbers k such that 4^k - 3^k - 2^k is prime.
8
2, 3, 13, 21, 231, 849, 885, 1225, 2955, 10171
OFFSET
1,1
COMMENTS
a(10) > 7500. - Derek Orr, Apr 08 2014
a(11) > 10^5. - Robert Price, Apr 20 2019
EXAMPLE
4^2 - 3^2 - 2^2 = 16 - 9 - 4 = 3.
MAPLE
A138699:=n->`if`(isprime(4^n - 3^n - 2^n), n, NULL); seq(A138699(n), n=1..1000); # Wesley Ivan Hurt, Apr 08 2014
MATHEMATICA
Select[Range[11^3], PrimeQ[4^# - 3^# - 2^# ]&]
PROG
(PARI) for(n=1, 7500, if(ispseudoprime(4^n - 3^n - 2^n), print1(n, ", "))) \\ Derek Orr, Apr 08 2014
CROSSREFS
Sequence in context: A136341 A139563 A019226 * A341713 A077248 A282342
KEYWORD
nonn,more,hard
AUTHOR
EXTENSIONS
a(9) from Derek Orr, Apr 08 2014
a(10) from Robert Price, Apr 20 2019
STATUS
approved