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 A119183 #7 Jul 13 2021 21:03:57
%S A119183 2,9,10,29,262,954,2590,2662,9534,25862,26662,82865,95334,104262,
%T A119183 266662,298514,2666662,10338610,26666662,30151462,103493337,266290989,
%U A119183 266666662,1043584537,2666666662,3302531009,10531233862,26288192537
%N A119183 Numbers k such that the k-th triangular number contains only digits {3,4,5}.
%H A119183 G. Resta, <a href="http://www.numbersaplenty.com/tr/tr345.html">Tridigital Triangular Numbers</a>
%Y A119183 Cf. A000217, A119182. See A119034 for a table of cross-references.
%K A119183 nonn,base
%O A119183 1,1
%A A119183 _Giovanni Resta_, May 10 2006