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A181569
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Greatest common divisor of n! and n+1.
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4
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1, 1, 2, 1, 6, 1, 8, 9, 10, 1, 12, 1, 14, 15, 16, 1, 18, 1, 20, 21, 22, 1, 24, 25, 26, 27, 28, 1, 30, 1, 32, 33, 34, 35, 36, 1, 38, 39, 40, 1, 42, 1, 44, 45, 46, 1, 48, 49, 50, 51, 52, 1, 54, 55, 56, 57, 58, 1, 60, 1, 62, 63, 64, 65, 66, 1, 68, 69, 70, 1, 72, 1, 74, 75, 76, 77, 78, 1
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OFFSET
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1,3
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COMMENTS
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From Wilson's theorem, it follows that a(n) = 1 when n + 1 is prime, a(n) > 1 otherwise. - Alonso del Arte, Feb 25 2014
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LINKS
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FORMULA
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for n > 3: a(n) = (n + 1) / (n*A010051(n+1) + 1).
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EXAMPLE
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a(6) = 1 because 6! and 7 are coprime.
a(7) = 8 because 7! = 5040 and gcd(5040, 8) = 8.
a(8) = 9 because 8! = 40320 and gcd(40320, 9) = 9.
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MAPLE
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MATHEMATICA
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PROG
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(PARI) a(n)= n!/denominator(polcoeff((x+1)*exp(x+x*O(x^n)), n)); \\ Gerry Martens, Aug 12 2015
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CROSSREFS
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KEYWORD
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nonn,easy
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AUTHOR
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STATUS
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approved
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