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 A023886 #21 Aug 26 2025 08:34:49 %S A023886 4,8,9,15,18,21,25,27,33,35,39,45,49,51,55,57,63,65,69,75,77,81,85,87, %T A023886 91,93,95,98,99,111,115,117,119,121,123,125,128,129,133,141,143,145, %U A023886 147,153,155,159,161,162,169,171,175,177,183,185,187,201,203 %N A023886 Average of proper divisors excluding 1 is an integer. %H A023886 Vincenzo Librandi, <a href="/A023886/b023886.txt">Table of n, a(n) for n = 1..1000</a> %t A023886 Select[Range[210],IntegerQ[Mean[Rest[Most[Divisors[#]]]]]&] (* _Harvey P. Dale_, Feb 20 2011 *) %K A023886 nonn,changed %O A023886 1,1 %A A023886 _Olivier Gérard_ %E A023886 Definition clarified by _Harvey P. Dale_, Feb 20 2011