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 A119073 #21 Mar 30 2023 23:34:32
%S A119073 6,66,406,666,66066,446040,600060,46046406,440466040,4040600460,
%T A119073 6604444400406,4440066066400004040,644006046066000066046,
%U A119073 44464646466606404046664666,464440406444064040044646006604604066,660466006640066446666000606004066646,60404640400640406040004460664400044060
%N A119073 Triangular numbers composed of digits {0,4,6}.
%H A119073 Giovanni Resta, <a href="http://www.numbersaplenty.com/tr/tr046.html">Tridigital Triangular Numbers</a>.
%F A119073 a(n) = A000217(A119074(n)). - _Tyler Busby_, Mar 27 2023
%t A119073 Rest[Select[FromDigits/@Tuples[{0, 4, 6}, 10], IntegerQ[(Sqrt[8 # + 1] - 1)/2] &]] (* _Vincenzo Librandi_, Dec 18 2015 *)
%o A119073 (Magma) [t: n in [1..2*10^7] | Set(Intseq(t)) subset {0,4,6} where t is n*(n+1) div 2]; // _Vincenzo Librandi_, Dec 18 2015
%Y A119073 Cf. A000217, A058438, A119074.
%Y A119073 See A119033 for a table of cross-references.
%K A119073 nonn,base
%O A119073 1,1
%A A119073 _Giovanni Resta_, May 10 2006
%E A119073 a(15)-a(16) from _Max Alekseyev_, May 10 2009
%E A119073 a(17) from _Tyler Busby_, Mar 27 2023