A248082 Least number k such that k^n - k +/- 1 are twin primes, or 0 if no such k exists.

3, 2, 6, 2, 4, 30, 0, 27, 4, 9, 109, 14, 0, 70, 58, 208, 12, 65, 0, 172, 1579, 1639, 585, 208, 0, 494, 505, 79, 3630, 95, 0, 81, 4422, 130, 1648, 3, 0, 13030, 174, 3, 627, 9524, 0, 3858, 1369, 1235, 11340, 6411, 0, 35494, 2553, 4883, 412, 44366, 0, 14640, 101386, 44021, 3003, 13045

Offset: 2

Author

Derek Orr, Sep 30 2014

Keywords

• nonn

Comments

For n > 2, if n == 2 (mod 6), then k^n - k + 1 is divisible by k^2 - k + 1. Thus it will never be prime.

Crossrefs

Cf. A131530, A236524, A236763.

Programs

PARI

a(n)=if(n>2&&n==Mod(2,6),return(0));k=1;while(!ispseudoprime(k^n-k+1)||!ispseudoprime(k^n-k-1),k++);k
n=2;while(n<100,print1(a(n),", ");n++)