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 A119223 #11 Mar 31 2023 03:20:29
%S A119223 3,10,11,34,36,105,109,114,3363,13834,438109,1383471,3622034,10954411,
%T A119223 11537388,33336636,105517363,141114114,3333366765,3333333366663363,
%U A119223 333645229535671903
%N A119223 Numbers k such that the k-th triangular number contains only digits {5,6,9}.
%H A119223 Giovanni Resta, <a href="http://www.numbersaplenty.com/tr/tr569.html">Tridigital Triangular Numbers</a>.
%Y A119223 Cf. A000217, A119222. See A119034 for a table of cross-references.
%K A119223 nonn,base,more
%O A119223 1,1
%A A119223 _Giovanni Resta_, May 10 2006
%E A119223 a(21) from _Tyler Busby_, Mar 31 2023