A138699 Numbers k such that 4^k - 3^k - 2^k is prime.

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

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 * A341713 A077248 A282342

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