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 A053868 #28 Jun 20 2021 03:11:10 %S A053868 2,3,4,5,7,8,11,13,15,16,17,18,19,21,23,27,29,31,32,33,35,36,37,39,41, %T A053868 43,45,47,50,51,53,55,57,59,61,63,64,65,67,69,71,72,73,75,77,79,83,85, %U A053868 87,89,91,93,95,97,98,99,100,101,103,105,107,109,111,113,115,117,119 %N A053868 Numbers whose sum of proper divisors is odd. %C A053868 Numbers which are twice squares, even squares or odd nonsquares. %H A053868 Reinhard Zumkeller, <a href="/A053868/b053868.txt">Table of n, a(n) for n = 1..10000</a> %o A053868 (Haskell) %o A053868 a053868 n = a053868_list !! (n-1) %o A053868 a053868_list = filter (odd . a001065) [1..] %o A053868 -- _Reinhard Zumkeller_, Nov 01 2015, Sep 15 2011 %Y A053868 Cf. A000203, A001065, A028982, A053869. %K A053868 nonn %O A053868 1,1 %A A053868 _Henry Bottomley_, Mar 29 2000 %E A053868 Improved name from _Omar E. Pol_, Aug 14 2009