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 A119142 #11 Mar 24 2023 03:03:08
%S A119142 1,6,66,666,861,116886,1188111,8166861,681118686,8186688861,
%T A119142 181886818816,616886668881,1611611188111,6188181818668868161,
%U A119142 8188686181116816661,61116116118118668181,686168618118116111616,1118166618111681811816,66861818861688166881668181
%N A119142 Triangular numbers composed of digits {1,6,8}.
%H A119142 Giovanni Resta, <a href="http://www.numbersaplenty.com/tr/tr168.html">Tridigital Triangular Numbers</a>
%F A119142 a(n) = A000217(A119143(n)). - _Michel Marcus_, Mar 24 2023
%Y A119142 Cf. A000217, A053909, A119143. See A119033 for a table of cross-references.
%K A119142 nonn,base
%O A119142 1,2
%A A119142 _Giovanni Resta_, May 10 2006
%E A119142 a(18)-a(19) from _Tyler Busby_, Mar 23 2023