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 A119071 #14 Mar 15 2023 07:53:30
%S A119071 45,55,4005,5050,404550,405450,500500,40405555,40504500,50005000,
%T A119071 454044045,500054500,4050045000,4540044405,5000050000,405000450000,
%U A119071 455005054540,500000500000,40500004500000,50000005000000,50450455004040,540550504445050,4050000045000000
%N A119071 Triangular numbers composed of digits {0,4,5}.
%H A119071 Giovanni Resta, <a href="http://www.numbersaplenty.com/tr/tr045.html">Tridigital Triangular Numbers</a>
%F A119071 a(n) = A000217(A119072(n)). - _Michel Marcus_, Mar 15 2023
%Y A119071 Cf. A000217, A058436, A119072. See A119033 for a table of cross-references.
%K A119071 nonn,base
%O A119071 1,1
%A A119071 _Giovanni Resta_, May 10 2006
%E A119071 a(21)-a(23) from _Tyler Busby_, Mar 14 2023