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 A119085 #13 Mar 31 2023 21:40:30
%S A119085 55,595,990,5050,5995,500500,50005000,50909095,50999950,505000090,
%T A119085 5000050000,500000500000,500999999500,955909595955,9055595509950,
%U A119085 50000005000000,59000000095590,95595999550590,5000000050000000,5000990099009950,5000990999099095
%N A119085 Triangular numbers composed of digits {0,5,9}.
%H A119085 Giovanni Resta, <a href="http://www.numbersaplenty.com/tr/tr059.html">Tridigital Triangular Numbers</a>.
%F A119085 a(n) = A000217(A119086(n)). - _Tyler Busby_, Mar 31 2023
%t A119085 Rest[Select[FromDigits/@Tuples[{0,5,9},16],OddQ[Sqrt[8#+1]]&]] (* _Harvey P. Dale_, Apr 14 2019 *)
%Y A119085 Cf. A000217, A058448, A119086. See A119033 for a table of cross-references.
%K A119085 nonn,base
%O A119085 1,1
%A A119085 _Giovanni Resta_, May 10 2006
%E A119085 a(20)-a(21) from _Tyler Busby_, Mar 23 2023