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 A119139 #8 Jul 13 2021 07:28:36
%S A119139 1,5,10,13,34,101,109,138,1738,10114,19794,1011090,1019010,1054130,
%T A119139 1091010,34406858,178858133,565606858,4289521091010,55841058721258
%N A119139 Numbers k such that the k-th triangular number contains only digits {1,5,9}.
%C A119139 Next term exceeds 1.4*10^16.
%H A119139 G. Resta, <a href="http://www.numbersaplenty.com/tr/tr159.html">Tridigital Triangular Numbers</a>
%Y A119139 Cf. A000217, A119138. See A119034 for a table of cross-references.
%K A119139 nonn,base,more
%O A119139 1,2
%A A119139 _Giovanni Resta_, May 10 2006