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 A119213 #7 Jul 13 2021 21:30:38
%S A119213 3,11,36,131,411,1331,13331,35963,113916,133331,1333331,13333331,
%T A119213 133333331,1333333331,13333333331,31141241043,133333333331,
%U A119213 1333333333331,4110641475211,13333333333331,133333333333331
%N A119213 Numbers k such that the k-th triangular number contains only digits {4,6,8}.
%H A119213 G. Resta, <a href="http://www.numbersaplenty.com/tr/tr468.html">Tridigital Triangular Numbers</a>
%Y A119213 Cf. A000217, A119212. See A119034 for a table of cross-references.
%K A119213 nonn,base
%O A119213 1,1
%A A119213 _Giovanni Resta_, May 10 2006