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 A119191 #7 Jul 13 2021 21:28:54
%S A119191 2,10,129,841229,26014826114,3417172921745,10520014765729
%N A119191 Numbers k such that the k-th triangular number contains only digits {3,5,8}.
%C A119191 Next term exceeds 1.4*10^16.
%H A119191 G. Resta, <a href="http://www.numbersaplenty.com/tr/tr358.html">Tridigital Triangular Numbers</a>
%Y A119191 Cf. A000217, A119190. See A119034 for a table of cross-references.
%K A119191 nonn,base,more
%O A119191 1,1
%A A119191 _Giovanni Resta_, May 10 2006