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 A043504 #23 Apr 24 2021 21:29:40 %S A043504 3333,13333,23333,30333,31333,32333,33033,33133,33233,33303,33313, %T A043504 33323,33330,33331,33332,33334,33335,33336,33337,33338,33339,33343, %U A043504 33353,33363,33373,33383,33393,33433,33533,33633,33733 %N A043504 Numbers having four 3's in base 10. %H A043504 Daniel Starodubtsev, <a href="/A043504/b043504.txt">Table of n, a(n) for n = 1..10000</a> %t A043504 Select[Range[34000],DigitCount[#,10,3]==4&] (* _Harvey P. Dale_, Feb 02 2011 *) %Y A043504 Subsequence of A011533. %K A043504 nonn,base %O A043504 1,1 %A A043504 _Clark Kimberling_