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 A119176 #12 Apr 06 2023 21:41:54
%S A119176 6,66,666,2926,29962999696266,226966926929226,9996922966699222296,
%T A119176 296292269222296622226,22266696966226666966622226,
%U A119176 266669269626696962299266226222926
%N A119176 Triangular numbers composed of digits {2,6,9}.
%C A119176 a(11) > 10^40. - _Tyler Busby_, Mar 28 2023
%H A119176 Giovanni Resta, <a href="http://www.numbersaplenty.com/tr/tr269.html">Tridigital Triangular Numbers</a>.
%F A119176 a(n) = A000217(A119177(n)). - _Tyler Busby_, Mar 28 2023
%Y A119176 Cf. A000217, A053931, A119177. See A119033 for a table of cross-references.
%K A119176 nonn,base,more
%O A119176 1,1
%A A119176 _Giovanni Resta_, May 10 2006
%E A119176 a(10) from _Tyler Busby_, Mar 28 2023