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 A119118 #10 Jul 13 2021 07:32:17
%S A119118 1,2,18,58,1853,5853,1620578,485216058,1243473981,2747265466,
%T A119118 595277030253,789599540493,2573455929746,48450258487106
%N A119118 Numbers k such that the k-th triangular number contains only digits {1,3,7}.
%C A119118 Next term is greater than 4.4*10^18. - _Max Alekseyev_, Oct 15 2012
%H A119118 G. Resta, <a href="http://www.numbersaplenty.com/tr/tr137.html">Tridigital Triangular Numbers</a>
%Y A119118 Cf. A000217, A119117. See A119034 for a table of cross-references.
%K A119118 nonn,base,more
%O A119118 1,2
%A A119118 _Giovanni Resta_, May 10 2006