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 A119149 #8 Jul 13 2021 07:26:41
%S A119149 1,13,18,58,586,1258,58613,1350538,1414213,59517693,1398413386,
%T A119149 5996665693,119976657489461
%N A119149 Numbers k such that the k-th triangular number contains only digits {1,7,9}.
%C A119149 Next term exceeds 1.4*10^16.
%H A119149 G. Resta, <a href="http://www.numbersaplenty.com/tr/tr179.html">Tridigital Triangular Numbers</a>
%Y A119149 Cf. A000217, A119148. See A119034 for a table of cross-references.
%K A119149 nonn,base,more
%O A119149 1,2
%A A119149 _Giovanni Resta_, May 10 2006