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 A119172 #12 May 27 2023 18:40:05
%S A119172 6,66,276,666,7626,6666726,77666666626,2662627722726,2777672627676766,
%T A119172 77772662277672726,6622726277766676626,672667762262676277666726
%N A119172 Triangular numbers composed of digits {2,6,7}.
%C A119172 a(13) > 10^40. - _Tyler Busby_, Mar 29 2023
%H A119172 Giovanni Resta, <a href="http://www.numbersaplenty.com/tr/tr267.html">Tridigital Triangular Numbers</a>.
%F A119172 a(n) = A000217(A119173(n)). - _Tyler Busby_, Mar 29 2023
%Y A119172 Cf. A000217, A058462, A119173. See A119033 for a table of cross-references.
%K A119172 nonn,base,more
%O A119172 1,1
%A A119172 _Giovanni Resta_, May 10 2006