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 A119146 #11 Apr 01 2023 09:11:24
%S A119146 1,78,171,1711,8778,11781,887778,1188111,18111171,71778171,88877778,
%T A119146 811178781,7781717881,8888777778,181877771881,887788118778,
%U A119146 888887777778,88877878118778,88888877777778,181887881178871,8888778778118778,8888888777777778,117888788817817111
%N A119146 Triangular numbers composed of digits {1,7,8}.
%H A119146 Giovanni Resta, <a href="http://www.numbersaplenty.com/tr/tr178.html">Tridigital Triangular Numbers</a>.
%F A119146 a(n) = A000217(A119147(n)). - _Tyler Busby_, Mar 31 2023
%Y A119146 Cf. A000217, A053913, A119147. See A119033 for a table of cross-references.
%K A119146 nonn,base
%O A119146 1,2
%A A119146 _Giovanni Resta_, May 10 2006
%E A119146 a(21)-a(23) from _Tyler Busby_, Mar 22 2023