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 A119179 #8 Jul 13 2021 07:23:33
%S A119179 7,12,67,132,667,1287,1332,4067,6667,13287,13332,66667,75932,133287,
%T A119179 133332,666667,1333287,1333332,6666667,13333287,13333332,21395692,
%U A119179 23335692,23335932,66666667,124280507,124721912,133333287,133333332
%N A119179 Numbers k such that the k-th triangular number contains only digits {2,7,8}.
%H A119179 G. Resta, <a href="http://www.numbersaplenty.com/tr/tr278.html">Tridigital Triangular Numbers</a>
%Y A119179 Cf. A000217, A119178. See A119034 for a table of cross-references.
%K A119179 nonn,base
%O A119179 1,1
%A A119179 _Giovanni Resta_, May 10 2006