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 A119174 #12 Mar 31 2023 02:49:20
%S A119174 6,28,66,666,2628,228826,828828,2222886,66268828,222868828,286262628,
%T A119174 628262628,688668828,862266628,2266226826,622686668286628,
%U A119174 866688628826628,68262228626828682628,288626826822666288666,66288228282628868868828,28622882886686262262866288686266
%N A119174 Triangular numbers composed of digits {2,6,8}.
%H A119174 Giovanni Resta, <a href="http://www.numbersaplenty.com/tr/tr268.html">Tridigital Triangular Numbers</a>.
%F A119174 a(n) = A000217(A119175(n)). - _Tyler Busby_, Mar 28 2023
%Y A119174 Cf. A000217, A119175. See A119033 for a table of cross-references.
%K A119174 nonn,base
%O A119174 1,1
%A A119174 _Giovanni Resta_, May 10 2006
%E A119174 a(20)-a(21) from _Tyler Busby_, Mar 28 2023