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 A039003 #17 Jun 26 2021 06:45:09 %S A039003 1,3,5,7,8,13,15,18,21,23,24,29,31,33,35,36,44,50,53,55,56,61,63,70, %T A039003 73,75,78,82,85,87,88,93,95,97,99,100,108,114,117,119,120,125,127,130, %U A039003 133,135,136,141,143,145,147,148,156,160,177,179,180,188,198,201,203 %N A039003 Numbers whose base-4 representation has the same number of 0's and 2's. %H A039003 Daniel Starodubtsev, <a href="/A039003/b039003.txt">Table of n, a(n) for n = 1..10000</a> %Y A039003 Cf. A007090, A160380, A160382. %K A039003 nonn,base,easy %O A039003 1,2 %A A039003 _Olivier Gérard_