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A274382
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a(n) = gcd(n, n*(n+1)/2 - sigma(n)).
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2
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1, 2, 1, 1, 1, 3, 1, 1, 1, 1, 1, 2, 1, 1, 3, 1, 1, 6, 1, 4, 1, 1, 1, 24, 1, 1, 1, 14, 1, 3, 1, 1, 3, 1, 1, 1, 1, 1, 1, 10, 1, 3, 1, 2, 3, 1, 1, 4, 1, 2, 3, 4, 1, 3, 1, 4, 1, 1, 1, 6, 1, 1, 1, 1, 1, 3, 1, 4, 3, 1, 1, 3, 1, 1, 1, 2, 1, 3, 1, 2, 1, 1, 1, 14, 1, 1
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OFFSET
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1,2
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LINKS
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FORMULA
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EXAMPLE
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a(6) = 3 because 6*7/2 - sigma(6) = 21 - 12 = 9 and gcd(6,9) = 3.
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MAPLE
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with(numtheory); P:=proc(q) local n;
for n from 1 to q do print(gcd(n, n*(n+1)/2-sigma(n))); od; end: P(10^3);
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MATHEMATICA
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Table[GCD[n, n (n+1)/2 - DivisorSigma[1, n]], {n, 100}] (* Vincenzo Librandi, Jun 25 2016 *)
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PROG
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(PARI) a(n) = gcd(n, n*(n+1)/2-sigma(n)) \\ Felix Fröhlich, Jun 23 2016
(Magma) [GCD(n, n*(n+1) div 2-SumOfDivisors(n)): n in [1..100]]; // Vincenzo Librandi, Jun 25 2016
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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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