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 A119047 #11 Mar 14 2023 12:59:30
%S A119047 1,10,91,190,990,10011,19110,19900,90100,1911990,1991010,1999000,
%T A119047 99991011,199110990,199910010,199990000,901999101,1000900911,
%U A119047 1111019091,19991100990,19999100010,19999900000,1999911000990,1999991000010,1999999000000,11109109109010
%N A119047 Triangular numbers composed of digits {0,1,9}.
%H A119047 Giovanni Resta, <a href="http://www.numbersaplenty.com/tr/tr019.html">Tridigital Triangular Numbers</a>
%F A119047 a(n) = A000217(A119048(n)). - _Michel Marcus_, Mar 14 2023
%Y A119047 Cf. A000217, A119048. See A119033 for a table of cross-references.
%K A119047 nonn,base
%O A119047 1,2
%A A119047 _Giovanni Resta_, May 10 2006
%E A119047 a(24)-a(26) from _Tyler Busby_, Mar 14 2023