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%I #35 Sep 08 2022 08:46:17
%S 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,
%T 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,
%U 4,3,1,1,3,1,1,1,2,1,3,1,2,1,1,1,14,1,1
%N a(n) = gcd(n, n*(n+1)/2 - sigma(n)).
%H Paolo P. Lava, <a href="/A274382/b274382.txt">Table of n, a(n) for n = 1..10000</a>
%F a(n) = gcd(n, A000217(n)-A000203(n)). - _Felix Fröhlich_, Jun 23 2016
%F a(n) = gcd(n, antisigma(n)) = gcd(n, A024816(n)). - _Omar E. Pol_, Jun 29 2016
%e a(6) = 3 because 6*7/2 - sigma(6) = 21 - 12 = 9 and gcd(6,9) = 3.
%p with(numtheory); P:=proc(q) local n;
%p for n from 1 to q do print(gcd(n,n*(n+1)/2-sigma(n))); od; end: P(10^3);
%t Table[GCD[n, n (n+1)/2 - DivisorSigma[1, n]], {n, 100}] (* _Vincenzo Librandi_, Jun 25 2016 *)
%o (PARI) a(n) = gcd(n, n*(n+1)/2-sigma(n)) \\ _Felix Fröhlich_, Jun 23 2016
%o (Magma) [GCD(n, n*(n+1) div 2-SumOfDivisors(n)): n in [1..100]]; // _Vincenzo Librandi_, Jun 25 2016
%Y Cf. A009194, A024816.
%K nonn,easy
%O 1,2
%A _Paolo P. Lava_, Jun 23 2016
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