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 A119231 #7 Jul 13 2021 21:31:39
%S A119231 3,11,12,36,116,132,1163,1332,13332,133332,1333332,3941747,11737707,
%T A119231 13333332,133333332,1333333332,13333333332,133333333332,416381478667,
%U A119231 1254414499811,1333333333332,4187521168132,11635005525283
%N A119231 Numbers k such that the k-th triangular number contains only digits {6,7,8}.
%H A119231 G. Resta, <a href="http://www.numbersaplenty.com/tr/tr678.html">Tridigital Triangular Numbers</a>
%Y A119231 Cf. A000217, A119230. See A119034 for a table of cross-references.
%K A119231 nonn,base
%O A119231 1,1
%A A119231 _Giovanni Resta_, May 10 2006