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 A039006 #27 Jun 20 2021 14:54:01 %S A039006 0,1,4,5,11,14,16,17,20,21,27,30,35,39,44,45,50,54,56,57,64,65,68,69, %T A039006 75,78,80,81,84,85,91,94,99,103,108,109,114,118,120,121,131,135,140, %U A039006 141,147,151,156,157,175,176,177,180,181,187,190,194,198,200,201,210 %N A039006 Numbers whose base-4 representation has the same number of 2's and 3's. %H A039006 Daniel Starodubtsev, <a href="/A039006/b039006.txt">Table of n, a(n) for n = 1..10000</a> %t A039006 Select[Range[0,250],DigitCount[#,4,2]==DigitCount[#,4,3]&] (* _Harvey P. Dale_, Mar 19 2017 *) %Y A039006 Cf. A007090, A160382, A160383, A039005. %Y A039006 Cf. A000302, A052539 (subsequences). %K A039006 nonn,base,easy %O A039006 1,3 %A A039006 _Olivier Gérard_