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a(n) is the largest nonnegative integer m such that 2*n*k-1 is prime for all k where 1<=k<=m. a(n) = 0 if 2n-1 is composite.
1

%I #6 Apr 09 2014 10:16:34

%S 0,3,5,1,0,2,1,0,1,1,0,3,0,0,3,1,0,0,1,0,2,1,0,1,0,0,2,0,0,1,1,0,0,1,

%T 0,1,1,0,0,1,0,3,0,0,5,0,0,0,1,0,1,1,0,1,1,0,2,0,0,0,0,0,0,1,0,2,0,0,

%U 1,1,0,0,0,0,1,1,0,0,1,0,0,1,0,1,0,0,3,0,0,2,1,0,0,0,0,2,1,0,1,1,0,0,0,0,0

%N a(n) is the largest nonnegative integer m such that 2*n*k-1 is prime for all k where 1<=k<=m. a(n) = 0 if 2n-1 is composite.

%e For n = 3: 2*3*1 -1 = 5, which is prime. 2*3*2 - 1 = 11, which is prime. 2*3*3 - 1 = 17, which is prime. 2*3*4 -1 = 23, which is prime. 2*3*5 -1 = 29, which is prime. But 2*3*6 - 1 = 35, which is composite. So a(3) = 5, because there are 5 primes in the arithmetic sequence before hitting a composite.

%Y A146524

%K nonn

%O 1,2

%A _Leroy Quet_, Oct 30 2008

%E Extended by _Ray Chandler_, Nov 01 2008