A157341 Least number k such that 6*k^n-1 is prime, with k>1 when n>1.

1, 2, 2, 10, 2, 2, 3, 20, 22, 2, 3, 220, 9, 8, 30, 120, 2, 7, 3, 45, 4, 3, 10, 125, 8, 3, 4, 5, 77, 108, 8, 30, 2, 3, 35, 15, 2, 35, 53, 10, 32, 2, 32, 50, 37, 12, 17, 215, 73, 45, 4, 55, 43, 2, 3, 715, 42, 70, 33, 160, 3, 90, 2, 745, 5, 38, 3, 40, 7, 295, 4, 5, 10, 70, 2, 90, 138, 32, 60

Offset: 1

Author

Pierre CAMI, Feb 27 2009

Keywords

• nonn

Links

• Marius A. Burtea, Table of n, a(n) for n = 1..230

Crossrefs

Cf. A164523 (where a(n)=2).

Programs

Magma

sol:=[1]; for n in [2..80] do k:=2;  while not IsPrime(6*k^n-1) do k:=k+1; end while; Append(~sol,k); end for; sol; // Marius A. Burtea, Sep 15 2019

PARI

a(n) = {my(k); if (n>1, k = 2, k = 1); while (!isprime(6*k^n-1), k++); k;} \\ Michel Marcus, Sep 15 2019

Extensions

Corrected by Pierre CAMI, Mar 09 2009

Name clarified by Michel Marcus, Sep 15 2019