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 A119225 #7 Jul 13 2021 21:32:12
%S A119225 10,12,107,125,132,389,1332,3892,10572,10749,13250,13332,105714,
%T A119225 133332,1255050,1333332,4208987,13333332,107497707,133333332,
%U A119225 1054396107,1333333332,10843226972,13333333332,133333333332
%N A119225 Numbers k such that the k-th triangular number contains only digits {5,7,8}.
%H A119225 G. Resta, <a href="http://www.numbersaplenty.com/tr/tr578.html">Tridigital Triangular Numbers</a>
%Y A119225 Cf. A000217, A119224. See A119034 for a table of cross-references.
%K A119225 nonn,base
%O A119225 1,1
%A A119225 _Giovanni Resta_, May 10 2006