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 A119072 #8 Jul 13 2021 01:25:16
%S A119072 9,10,89,100,899,900,1000,8989,9000,10000,30134,31624,90000,95289,
%T A119072 100000,900000,953944,1000000,9000000,10000000,10044944,32880100,
%U A119072 90000000,100000000,900000000,1000000000,3328800100,9000000000
%N A119072 Numbers k such that the k-th triangular number contains only digits {0,4,5}.
%H A119072 G. Resta, <a href="http://www.numbersaplenty.com/tr/tr045.html">Tridigital Triangular Numbers</a>
%Y A119072 Cf. A000217, A119071. See A119034 for a table of cross-references.
%K A119072 nonn,base
%O A119072 1,1
%A A119072 _Giovanni Resta_, May 10 2006