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A146525
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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.
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1
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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, 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, 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
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OFFSET
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1,2
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LINKS
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EXAMPLE
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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.
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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