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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 3,1,3,0,1,1,0,1,2,0,1,0,0,1,2,0,0,3,0,1,1,0,1,0,0,1,0,0,1,1,0,0,1,0,

%T 1,1,0,0,2,0,1,0,0,1,0,0,0,2,0,1,1,0,1,1,0,1,0,0,0,0,0,0,1,0,1,0,0,1,

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

%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 = 7, which is prime. 2*3*2 + 1 = 13, which is prime. 2*3*3 + 1 = 19, which is prime. But 2*3*4 + 1 = 25, which is composite. So a(3) = 3, because there are 3 primes in the arithmetic sequence before hitting a composite.

%Y A146525

%K nonn

%O 1,1

%A _Leroy Quet_, Oct 30 2008

%E Extended by _Ray Chandler_, Nov 01 2008