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A182936
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Greatest common divisor of the proper divisors of n, 0 if there are none.
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4
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0, 0, 0, 2, 0, 1, 0, 2, 3, 1, 0, 1, 0, 1, 1, 2, 0, 1, 0, 1, 1, 1, 0, 1, 5, 1, 3, 1, 0, 1, 0, 2, 1, 1, 1, 1, 0, 1, 1, 1, 0, 1, 0, 1, 1, 1, 0, 1, 7, 1, 1, 1, 0, 1, 1, 1, 1, 1, 0, 1, 0, 1, 1, 2, 1, 1, 0, 1, 1, 1, 0, 1, 0, 1, 1, 1, 1, 1, 0, 1, 3, 1, 0, 1, 1, 1, 1, 1, 0, 1, 1, 1, 1, 1, 1, 1, 0, 1, 1, 1, 0, 1, 0, 1, 1
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OFFSET
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1,4
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COMMENTS
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Here a proper divisor d of n is a divisor of n such that 1 < d < n.
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LINKS
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FORMULA
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a(n) = 0 if n is not composite, p if n is a proper power of prime p, and 1 otherwise. - Franklin T. Adams-Watters, Mar 22 2011
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MAPLE
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A182936 := n -> igcd(op(numtheory[divisors](n) minus {1, n}));
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MATHEMATICA
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Join[{0}, Table[GCD@@Most[Rest[Divisors[n]]], {n, 2, 110}]] (* Harvey P. Dale, May 04 2018 *)
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PROG
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(PARI) A182936(n) = { my(divs=divisors(n)); if(#divs<3, 0, gcd(vector(numdiv(n)-2, k, divs[k+1]))); }; \\ Antti Karttunen, Sep 23 2017
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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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