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 A239886 #17 Jul 01 2022 06:48:24 %S A239886 4,8,16,18,27,32,36,50,64,72,100,105,128,144,162,200,243,256,288,300, %T A239886 324,375,392,400,512,576,648,700,800,850,1024,1100,1134,1152,1200, %U A239886 1296,1350,1352,1458,1600,1620,1650,2048,2187,2304,2592,2850,2916,3078,3100,3125 %N A239886 Composite numbers whose proper divisor balance is an integer. %C A239886 This list excludes 1 and prime numbers, which by definition have no proper divisors. %H A239886 Amiram Eldar, <a href="/A239886/b239886.txt">Table of n, a(n) for n = 1..1000</a> (terms 1..267 from Vincenzo Librandi) %F A239886 Proper divisor balance of n = Sum_{1 < d < n and divides n} {d / phi(d)} where phi is Euler's phi function. %t A239886 Select[Range[2000], Function[ n, ! PrimeQ[n] && %t A239886 IntegerQ[Plus @@ Map[#/EulerPhi[#] &, DeleteCases[Divisors[n], 1 | n]]]]] %t A239886 q[n_] := CompositeQ[n] && IntegerQ[DivisorSum[n, #/EulerPhi[#] &, 1 < # < n &]]; Select[Range[4000], q] (* _Amiram Eldar_, Jul 01 2022 *) %Y A239886 Cf. A239887 (corresponding values of the proper divisor balance). %Y A239886 Cf. A000010, A023898, A023899 for the versions with all divisors included. %K A239886 nonn %O A239886 1,1 %A A239886 _Olivier Gérard_, Mar 29 2014