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 A119086 #8 Jul 13 2021 01:25:40
%S A119086 10,34,44,100,109,1000,10000,10090,10099,31780,100000,1000000,1000999,
%T A119086 1382685,4255724,10000000,10862780,13827219,100000000,100009900,
%U A119086 100009909,100009955,100009999,100901000,1000000000,10000000000
%N A119086 Numbers k such that the k-th triangular number contains only digits {0,5,9}.
%H A119086 G. Resta, <a href="http://www.numbersaplenty.com/tr/tr059.html">Tridigital Triangular Numbers</a>
%Y A119086 Cf. A000217, A119085. See A119034 for a table of cross-references.
%K A119086 nonn,base
%O A119086 1,1
%A A119086 _Giovanni Resta_, May 10 2006