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 A119051 #11 Mar 31 2023 13:21:11
%S A119051 55,5050,25200,255255,500500,50005000,525220255,2250500505,5000050000,
%T A119051 22052205055,500000500000,520022025225,2205022050055,2225205025200,
%U A119051 5220005220550,50000005000000,220500220500055,550250022200005,2552552000225055,5000000050000000
%N A119051 Triangular numbers composed of digits {0,2,5}.
%H A119051 Giovanni Resta, <a href="http://www.numbersaplenty.com/tr/tr025.html">Tridigital Triangular Numbers</a>.
%F A119051 a(n) = A000217(A119052(n)). - _Tyler Busby_, Mar 31 2023
%Y A119051 Cf. A000217, A058426, A119052. See A119033 for a table of cross-references.
%K A119051 nonn,base
%O A119051 1,1
%A A119051 _Giovanni Resta_, May 10 2006
%E A119051 a(19)-a(20) from _Tyler Busby_, Mar 22 2023