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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, 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 (list; graph; refs; listen; history; text; internal format)
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: A127124 A127136 A239101 * 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

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Last modified October 15 03:28 EDT 2019. Contains 328025 sequences. (Running on oeis4.)