A107709 - OEIS

%I #8 Mar 31 2012 13:22:04

%S 3,3,3,7,43,19,13,5,571,3,137,59,3823,2707,6277,1063,4523,631,8209,

%T 34537,102329,46399,30323,18803,1063,21019

%N Least odd prime a(n) such that (a(n)*M(n))^2 + a(n)*M(n) - 1 is prime with M(n) = Mersenne-primes (A000043).

%e M(1)=2^2-1=3, (3*3)^2 + 3*3 -1 = 89 prime so a(1)=3

%e M(2)=2^3-1=7, (3*7)^2 + 3*7 -1 = 461 prime so a(2)=3

%e M(3)=2^5-1=31, (3*31)^2 + 3*31 -1 = 8741 prime so a(3)=3

%e M(4)=2^7-1=127,(7*127)^2 + 7*127 -1 = 791209 prime so a(4)=7

%Y Cf. A000043.

%K hard,more,nonn

%O 1,1

%A _Pierre CAMI_, Jun 10 2005

%E More terms from Pierre CAMI, Nov 21 2011