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A097009
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a(n) = gcd(prime(2*n)-1, prime(n)-1).
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2
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1, 2, 4, 6, 2, 12, 2, 2, 2, 14, 6, 4, 20, 2, 2, 26, 2, 30, 6, 2, 36, 6, 2, 2, 12, 2, 2, 2, 54, 56, 2, 10, 4, 6, 4, 2, 12, 2, 2, 4, 2, 36, 2, 24, 14, 2, 70, 2, 2, 12, 4, 2, 48, 2, 8, 2, 2, 10, 2, 14, 6, 2, 2, 2, 12, 2, 6, 48, 2, 4, 4, 2, 2, 4, 2, 2, 2, 2, 16, 4, 2, 10, 2, 12, 2, 34, 8, 8, 20, 6, 2, 2
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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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a(3) = gcd(Prime(6)-1, prime(3)-1) = gcd(13-1, 5-1) = gcd(12, 4) = 4.
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MATHEMATICA
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PROG
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(Magma) [Gcd(NthPrime(2*n)-1, NthPrime(n)-1): n in [1..80]]; // Vincenzo Librandi, Dec 04 2015
(PARI) a(n) = gcd(prime(2*n)-1, prime(n)-1); \\ Michel Marcus, Dec 04 2015
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CROSSREFS
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Cf. A066978 (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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