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 A119093 #11 Apr 06 2023 02:19:28
%S A119093 78,780,8778,887778,88877778,870800778,7007800078,8008780080,
%T A119093 8888777778,770800800078,888887777778,70870887770880,88888877777778,
%U A119093 7808778880700878,8888888777777778,888888887777777778,70888000778807080078,88888888877777777778
%N A119093 Triangular numbers composed of digits {0,7,8}.
%H A119093 Giovanni Resta, <a href="http://www.numbersaplenty.com/tr/tr078.html">Tridigital Triangular Numbers</a>.
%F A119093 a(n) = A000217(A119094(n)). - _Tyler Busby_, Mar 31 2023
%Y A119093 Cf. A000217, A119094. See A119033 for a table of cross-references.
%K A119093 nonn,base
%O A119093 1,1
%A A119093 _Giovanni Resta_, May 10 2006
%E A119093 a(17)-a(18) from _Tyler Busby_, Mar 23 2023