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 A119210 #13 Mar 29 2023 17:19:55
%S A119210 6,66,666,476776,764466,4646676,464774774646,
%T A119210 667474767766464747666467446,7666777767444444644744476476,
%U A119210 44774674766666676747766477446
%N A119210 Triangular numbers composed of digits {4,6,7}.
%C A119210 a(11) > 10^40. - _Tyler Busby_, Mar 29 2023
%H A119210 Giovanni Resta, <a href="http://www.numbersaplenty.com/tr/tr467.html">Tridigital Triangular Numbers</a>.
%F A119210 a(n) = A000217(A119211(n)). - _Michel Marcus_, Mar 27 2023
%Y A119210 Cf. A000217, A053957, A119211. See A119033 for a table of cross-references.
%K A119210 nonn,base,more
%O A119210 1,1
%A A119210 _Giovanni Resta_, May 10 2006