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

Author

Vladimir Joseph Stephan Orlovsky, May 15 2008

Keywords

• nonn
• more
• hard

Comments

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

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

Examples

			4^2 - 3^2 - 2^2 = 16 - 9 - 4 = 3.
		

Programs

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^# ]&]

PARI

for(n=1, 7500, if(ispseudoprime(4^n - 3^n - 2^n), print1(n, ", "))) \\ Derek Orr, Apr 08 2014

Extensions

a(9) from Derek Orr, Apr 08 2014

a(10) from Robert Price, Apr 20 2019