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A290839
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a(n) = smallest prime p such that 2p + 2n - 1 is prime.
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2
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2, 2, 2, 3, 2, 2, 3, 2, 2, 3, 2, 5, 3, 2, 2, 7, 3, 2, 3, 2, 2, 3, 2, 7, 3, 2, 5, 3, 2, 2, 7, 3, 2, 3, 2, 2, 13, 3, 2, 3, 2, 11, 3, 2, 5, 7, 3, 2, 3, 2, 2, 3, 2, 2, 3, 2, 13, 7, 11, 5, 19, 3, 2, 3, 2, 5, 3, 2, 2, 7, 5, 5, 3, 2, 2, 7, 3, 2, 13, 3, 2, 3, 2, 7, 3, 2
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OFFSET
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0,1
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LINKS
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FORMULA
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MATHEMATICA
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Table[j=0; found=False; While[!found, j++; found=PrimeQ[2Prime[j]+2n-1]]; Prime[j], {n, 85}]
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PROG
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(PARI) a(n) = {my(p=2); while(!isprime(2*p+2*n-1), p = nextprime(p+1)); p; } \\ Michel Marcus, Aug 12 2017
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CROSSREFS
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Cf. A067076 (indices n at which a(n) = 2).
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KEYWORD
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nonn,easy
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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