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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 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

a(10) > 7500. - Derek Orr, Apr 08 2014

a(11) > 10^5. - Robert Price, Apr 20 2019

LINKS

Table of n, a(n) for n=1..10.

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 * A077248 A282342 A137248

Adjacent sequences:  A138696 A138697 A138698 * A138700 A138701 A138702

KEYWORD

nonn,more,hard

AUTHOR

Vladimir Joseph Stephan Orlovsky, May 15 2008

EXTENSIONS

a(9) from Derek Orr, Apr 08 2014

a(10) from Robert Price, Apr 20 2019

STATUS

approved

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Last modified January 25 07:55 EST 2020. Contains 331241 sequences. (Running on oeis4.)