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 A119224 #10 Mar 27 2023 05:43:23
%S A119224 55,78,5778,7875,8778,75855,887778,7575778,55888878,57775875,87787875,
%T A119224 88877778,5587777755,8888777778,787575878775,888887777778,
%U A119224 8857787887578,88888877777778,5777878558877778,8888888777777778,555875575755575778,888888887777777778
%N A119224 Triangular numbers composed of digits {5,7,8}.
%H A119224 Giovanni Resta, <a href="http://www.numbersaplenty.com/tr/tr578.html">Tridigital Triangular Numbers</a>.
%F A119224 a(n) = A000217(A119225(n)). - _Tyler Busby_, Mar 26 2023
%Y A119224 Cf. A000217, A119225. See A119033 for a table of cross-references.
%K A119224 nonn,base
%O A119224 1,1
%A A119224 _Giovanni Resta_, May 10 2006
%E A119224 a(21)-a(22) from _Tyler Busby_, Mar 26 2023