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 A119120 #10 Jul 13 2021 07:32:12
%S A119120 1,2,421,1541,8753,150421,12914246,1327696379533,4034385661121,
%T A119120 605166395826533,16360402306368458,249752330575267378
%N A119120 Numbers k such that the k-th triangular number contains only digits {1,3,8}.
%C A119120 Next term exceeds 4.4*10^18.
%H A119120 G. Resta, <a href="http://www.numbersaplenty.com/tr/tr138.html">Tridigital Triangular Numbers</a>
%Y A119120 Cf. A000217, A119119. See A119034 for a table of cross-references.
%K A119120 nonn,base,more
%O A119120 1,2
%A A119120 _Giovanni Resta_, May 10 2006
%E A119120 Two more terms from _Max Alekseyev_, May 12 2009