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%I #28 Feb 20 2024 07:00:00
%S 77,1568,2768,4775040
%N Numbers n such that the sum of the anti-divisors of n = 2n.
%C See A066272 for definition of anti-divisor.
%C a(5) > 10^10 - _Hiroaki Yamanouchi_, Mar 18 2015
%t antiDivisorSum[n_] := Total[Select[Range[2, n - 1], Abs[Mod[n, #] - #/2] < 1 &]]
%t Select[Range[1, 1600], antiDivisorSum[#] == 2*# &] (* _Julien Kluge_, Sep 19 2016 *)
%o (Python)
%o from sympy import divisors
%o A073931 = [n for n in range(3,10**5) if sum([2*d for d in divisors(n) if n > 2*d and n % (2*d)] + [d for d in divisors(2*n-1) if n > d >=2 and n % d] + [d for d in divisors(2*n+1) if n > d >=2 and n % d]) == 2*n]
%o # _Chai Wah Wu_, Aug 13 2014
%Y Cf. A066417.
%K more,nonn
%O 1,1
%A _Jason Earls_, Sep 03 2002
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