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 A039562 #14 Jul 01 2021 03:38:05 %S A039562 0,27,30,39,45,54,57,75,78,99,108,114,120,135,141,147,156,177,180,198, %T A039562 201,210,216,225,228,267,270,291,300,306,312,387,396,432,450,456,480, %U A039562 519,525,531,540,561,564,579,588,624,705,708,720,774,777,786,792,801 %N A039562 Numbers whose base-4 representation has the same number of 1's, 2's and 3's. %H A039562 Harvey P. Dale, <a href="/A039562/b039562.txt">Table of n, a(n) for n = 1..1000</a> %t A039562 Select[Range[0,1000],Length[Union[Most[DigitCount[#,4]]]]==1&] (* _Harvey P. Dale_, Oct 04 2016 *) %Y A039562 Cf. A007090. %K A039562 nonn,base,easy %O A039562 1,2 %A A039562 _Olivier Gérard_