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 A119061 #9 Mar 14 2023 19:37:43
%S A119061 3,55,300,3003,5050,500500,50005000,5000050000,33050333550,
%T A119061 500000500000,3505500530535,50000005000000,53555035005300,
%U A119061 355300503533550,5000000050000000,50035505550330300,300555503500333305,500000000500000000,50000000005000000000
%N A119061 Triangular numbers composed of digits {0,3,5}.
%H A119061 Giovanni Resta, <a href="http://www.numbersaplenty.com/tr/tr035.html">Tridigital Triangular Numbers</a>
%F A119061 a(n) = A000217(A119062(n)). - _Michel Marcus_, Mar 14 2023
%Y A119061 Cf. A000217, A119062. See A119033 for a table of cross-references.
%K A119061 nonn,base
%O A119061 1,1
%A A119061 _Giovanni Resta_, May 10 2006
%E A119061 a(17)-a(19) from _Tyler Busby_, Mar 14 2023