A145983 a(n) = least k such that either 6*k*M(n)-1 or 6*k*M(n)+1 or both is prime, where M(i)= i-th Mersenne prime.

1, 1, 2, 1, 4, 2, 1, 14, 3, 43, 28, 19, 56, 14, 14, 26, 75, 138, 335, 417, 291, 571, 1508, 7887, 5893, 5863, 2877, 9803, 29975, 7857

Offset

1,3

Comments

All terms correspond to certified primes using PFGW from primeform group.

Links

Table of n, a(n) for n=1..30.

Example

6*1*(2^2-1)-1 = 17 is prime as is 19 so a(1) = 1. 6*1*(2^3-1)-1 = 41 is prime as is 43 so a(2) = 1. 6*1*(2^5-1)-1 = 185 is not prime and 187 is not prime; 6*2*(2^5-1)-1 = 381 is not prime but 383 is prime so a(3) = 2.

Crossrefs

Sequence in context: A127136 A239101 A362266 * A245025 A257495 A120025

Adjacent sequences: A145980 A145981 A145982 * A145984 A145985 A145986

Keyword

more,nonn

Author

Pierre CAMI, Oct 26 2008

Extensions

Edited by N. J. A. Sloane, Nov 27 2008 at the suggestion of R. J. Mathar.

Status

approved