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 A119129 #12 Jul 13 2021 07:28:18
%S A119129 1,478,1541,4866,988113,4216353,15155321,16977521,983990258,
%T A119129 531956543121,544826911685686,16843306612090658,127392946577229686
%N A119129 Numbers k such that the k-th triangular number contains only digits {1,4,8}.
%C A119129 Next term exceeds 1.4*10^20.
%H A119129 G. Resta, <a href="http://www.numbersaplenty.com/tr/tr148.html">Tridigital Triangular Numbers</a>
%Y A119129 Cf. A000217, A119128. See A119034 for a table of cross-references.
%K A119129 nonn,base,more
%O A119129 1,2
%A A119129 _Giovanni Resta_, May 10 2006
%E A119129 a(12)-a(13) from _Max Alekseyev_, Aug 16 2013