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 A119230 #11 Mar 27 2023 03:33:43
%S A119230 6,66,78,666,6786,8778,676866,887778,88877778,8888777778,888887777778,
%T A119230 7768686676878,68886888677778,88888877777778,8888888777777778,
%U A119230 888888887777777778,88888888877777777778,8888888888777777777778,86686767888666878787778,786777868668667866767766
%N A119230 Triangular numbers composed of digits {6,7,8}.
%H A119230 Giovanni Resta, <a href="http://www.numbersaplenty.com/tr/tr678.html">Tridigital Triangular Numbers</a>.
%F A119230 a(n) = A000217(A119231(n)). - _Tyler Busby_, Mar 26 2023
%Y A119230 Cf. A000217, A119231. See A119033 for a table of cross-references.
%K A119230 nonn,base
%O A119230 1,1
%A A119230 _Giovanni Resta_, May 10 2006
%E A119230 a(19)-a(20) from _Tyler Busby_, Mar 26 2023