A248081 Least number k such that k^n + k +/- 1 are twin primes, or 0 if no such k exists.

2, 2, 3, 2, 0, 8, 462, 0, 15, 3, 0, 30, 1500, 0, 30, 2, 0, 371, 11058, 0, 11289, 1599, 0, 4139, 44994, 0, 36951, 54, 0, 651, 2088, 0, 8841, 13061, 0, 81, 83406, 0, 20451, 3291, 0, 1821, 1128, 0, 122070, 20534, 0, 57852, 82875, 0, 15150, 132, 0, 515, 7215, 0, 37470, 2375, 0, 2340

Offset

1,1

Comments

For n > 2, if n == 2 (mod 3), then k^n + k + 1 is divisible by k^2 + k + 1. Thus it will never be prime.

Links

Table of n, a(n) for n=1..60.

Prog

(PARI)
a(n)=if(n>2&&n==Mod(2, 3), return(0)); k=1; while(!ispseudoprime(k^n+k-1)||!ispseudoprime(k^n+k+1), k++); k
n=1; while(n<50, print1(a(n), ", "); n++)

Crossrefs

Cf. A088485, A236526, A236760.

Sequence in context: A248079 A127638 A127639 * A259632 A304041 A238509

Adjacent sequences: A248078 A248079 A248080 * A248082 A248083 A248084

Keyword

nonn

Author

Derek Orr, Sep 30 2014

Status

approved