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 A039005 #33 Jun 20 2021 14:53:32 %S A039005 0,2,7,8,10,13,19,27,28,30,32,34,39,40,42,45,49,52,54,57,67,75,76,78, %T A039005 95,99,107,108,110,112,114,119,120,122,125,128,130,135,136,138,141, %U A039005 147,155,156,158,160,162,167,168,170,173,177,180,182,185,193,196,198 %N A039005 Numbers whose base-4 representation has the same number of 1's and 3's. %H A039005 Daniel Starodubtsev, <a href="/A039005/b039005.txt">Table of n, a(n) for n = 1..10000</a> %Y A039005 Cf. A007090, A160381, A160383. %Y A039005 Cf. A004171 (subsequence). %K A039005 nonn,base,easy %O A039005 1,2 %A A039005 _Olivier Gérard_