This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A073931 #28 Feb 20 2024 07:00:00 %S A073931 77,1568,2768,4775040 %N A073931 Numbers n such that the sum of the anti-divisors of n = 2n. %C A073931 See A066272 for definition of anti-divisor. %C A073931 a(5) > 10^10 - _Hiroaki Yamanouchi_, Mar 18 2015 %t A073931 antiDivisorSum[n_] := Total[Select[Range[2, n - 1], Abs[Mod[n, #] - #/2] < 1 &]] %t A073931 Select[Range[1, 1600], antiDivisorSum[#] == 2*# &] (* _Julien Kluge_, Sep 19 2016 *) %o A073931 (Python) %o A073931 from sympy import divisors %o A073931 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 A073931 # _Chai Wah Wu_, Aug 13 2014 %Y A073931 Cf. A066417. %K A073931 more,nonn %O A073931 1,1 %A A073931 _Jason Earls_, Sep 03 2002