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 A119234 #15 Mar 30 2023 05:18:27
%S A119234 6,66,666,68898988866,88698868996686886,696999969866686966889999889666
%N A119234 Triangular numbers composed of digits {6,8,9}.
%C A119234 a(7) > 10^37. - _Max Alekseyev_, Apr 30 2010
%C A119234 a(7) > 10^40. - _Tyler Busby_, Mar 29 2023
%H A119234 Giovanni Resta, <a href="http://www.numbersaplenty.com/tr/tr689.html">Tridigital Triangular Numbers</a>.
%F A119234 a(n) = A000217(A119235(n)). - _Michel Marcus_, Mar 27 2023
%Y A119234 Cf. A000217, A053975, A119235. See A119033 for a table of cross-references.
%K A119234 nonn,base,more
%O A119234 1,1
%A A119234 _Giovanni Resta_, May 10 2006