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 A119107 #9 Mar 23 2023 19:17:05
%S A119107 1,21,28,1128,2211,8128,118828,222111,821121,828828,881128,1188111,
%T A119107 1828828,22221111,28218828,88811128,1821212128,2222211111,8888111128,
%U A119107 222222111111,888881111128,22222221111111,88888811111128,1122211112118111,2222222211111111
%N A119107 Triangular numbers composed of digits {1,2,8}.
%H A119107 Giovanni Resta, <a href="http://www.numbersaplenty.com/tr/tr128.html">Tridigital Triangular Numbers</a>
%F A119107 a(n) = A000217(A119108(n)). - _Michel Marcus_, Mar 23 2023
%Y A119107 Cf. A000217, A053887, A119108. See A119033 for a table of cross-references.
%K A119107 nonn,base
%O A119107 1,2
%A A119107 _Giovanni Resta_, May 10 2006
%E A119107 a(24)-a(25) from _Tyler Busby_, Mar 23 2023