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 A119209 #7 Jul 13 2021 21:30:18
%S A119209 9,10,34,109,314,334,1090,3334,33334,141109,333334,436909,3333334,
%T A119209 4369314,31609965,33166234,33333334,333333334,3333333334,3464100314,
%U A119209 33316662334,33333333334,104828011090,301512701090,333333333334
%N A119209 Numbers k such that the k-th triangular number contains only digits {4,5,9}.
%H A119209 G. Resta, <a href="http://www.numbersaplenty.com/tr/tr459.html">Tridigital Triangular Numbers</a>
%Y A119209 Cf. A000217, A119208. See A119034 for a table of cross-references.
%K A119209 nonn,base
%O A119209 1,1
%A A119209 _Giovanni Resta_, May 10 2006