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 A119215 #7 Jul 13 2021 21:30:48
%S A119215 3,11,31,36,43,96953253343
%N A119215 Numbers k such that the k-th triangular number contains only digits {4,6,9}.
%C A119215 Next term exceeds 1.4*10^16.
%H A119215 G. Resta, <a href="http://www.numbersaplenty.com/tr/tr469.html">Tridigital Triangular Numbers</a>
%Y A119215 Cf. A000217, A119214. See A119034 for a table of cross-references.
%K A119215 nonn,base,more
%O A119215 1,1
%A A119215 _Giovanni Resta_, May 10 2006