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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

%I

%S 1,1,2,1,4,2,1,14,3,43,28,19,56,14,14,26,75,138,335,417,291,571,1508,

%T 7887,5893,5863,2877,9803,29975,7857

%N 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

%C All terms correspond to certified primes using PFGW from primeform group

%e 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.

%K more,nonn

%O 1,3

%A _Pierre CAMI_, Oct 26 2008

%E Edited by _N. J. A. Sloane_, Nov 27 2008 at the suggestion of R. J. Mathar.

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Last modified April 18 08:37 EDT 2019. Contains 322209 sequences. (Running on oeis4.)