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A066978
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a(n) = gcd(prime(2*n)+1, prime(n)+1).
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2
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1, 4, 2, 4, 6, 2, 2, 2, 2, 6, 16, 2, 6, 4, 6, 6, 20, 2, 4, 6, 2, 2, 4, 2, 2, 6, 4, 12, 2, 6, 2, 12, 6, 2, 50, 8, 2, 4, 2, 2, 2, 14, 12, 2, 2, 40, 4, 56, 6, 2, 18, 30, 2, 18, 86, 2, 10, 2, 2, 6, 2, 6, 2, 24, 2, 6, 2, 2, 4, 10, 6, 36, 8, 22, 4, 6, 6, 2, 6, 2, 6, 2, 24, 2, 2, 2, 2, 2, 6, 2, 156, 6, 2, 4
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OFFSET
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1,2
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COMMENTS
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Starting with a(2)=4, all terms are even. - Zak Seidov, Jul 16 2016
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LINKS
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EXAMPLE
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a(4) = gcd(prime(8) + 1, prime(4) + 1) = gcd(19 + 1, 7 + 1) = gcd(20, 8) = 4.
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MATHEMATICA
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PROG
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(PARI) { for (n=1, 1000, write("b066978.txt", n, " ", gcd(prime(2*n) + 1, prime(n) + 1)) ) } \\ Harry J. Smith, Apr 13 2010
(Magma) [Gcd(NthPrime(2*n)+1, NthPrime(n)+1): n in [1..80]]; // Vincenzo Librandi, Dec 04 2015
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CROSSREFS
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Cf. A097009 (gcd(prime(2*n) - 1, prime(n) - 1)).
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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