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 A119228 #11 Mar 27 2023 03:33:40
%S A119228 55,595,5995,555985,85989999559555,5558888585898885,
%T A119228 898989555999995895,559585958899855598985,988889885885555858595,
%U A119228 85889898559958558998859955,5595888555988988898588558558585,8589985889588895598998885898885995,88988559899558559855895555589855985
%N A119228 Triangular numbers composed of digits {5,8,9}.
%C A119228 a(14) > 10^40. - _Tyler Busby_, Mar 26 2023
%H A119228 Giovanni Resta, <a href="http://www.numbersaplenty.com/tr/tr589.html">Tridigital Triangular Numbers</a>.
%F A119228 a(n) = A000217(A119229(n)). - _Tyler Busby_, Mar 26 2023
%Y A119228 Cf. A000217, A058470, A119229. See A119033 for a table of cross-references.
%K A119228 nonn,base
%O A119228 1,1
%A A119228 _Giovanni Resta_, May 10 2006
%E A119228 a(12)-a(13) from _Tyler Busby_, Mar 26 2023