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 A119197 #7 Jul 13 2021 21:29:19
%S A119197 2,3,8,11,36,816,4211,13163,409483,1128391,2583163,87935963,356051588,
%T A119197 35683017483,87964636836,11566016486836,36978011484891
%N A119197 Numbers k such that the k-th triangular number contains only digits {3,6,8}.
%C A119197 Next term exceeds 1.4*10^16.
%H A119197 G. Resta, <a href="http://www.numbersaplenty.com/tr/tr368.html">Tridigital Triangular Numbers</a>
%Y A119197 Cf. A000217, A119196. See A119034 for a table of cross-references.
%K A119197 nonn,base,more
%O A119197 1,1
%A A119197 _Giovanni Resta_, May 10 2006