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 A119180 #11 Apr 06 2023 21:41:57
%S A119180 28,828828,9298828,99228828,2882992822228828,88992922889298828,
%T A119180 299282229288828999298828
%N A119180 Triangular numbers composed of digits {2,8,9}.
%C A119180 a(8) > 10^40. - _Tyler Busby_, Mar 29 2023
%H A119180 Giovanni Resta, <a href="http://www.numbersaplenty.com/tr/tr289.html">Tridigital Triangular Numbers</a>.
%F A119180 a(n) = A000217(A119181(n)). - _Tyler Busby_, Mar 29 2023
%Y A119180 Cf. A000217, A053935, A119181. See A119033 for a table of cross-references.
%K A119180 nonn,base,more
%O A119180 1,1
%A A119180 _Giovanni Resta_, May 10 2006