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 A119057 #16 Mar 28 2023 17:46:51
%S A119057 990,2090209222020090,92209290022092090,200290202090990220,
%T A119057 222020200990922029290
%N A119057 Triangular numbers composed of digits {0,2,9}.
%C A119057 a(6) > 10^40. - _Tyler Busby_, Mar 28 2023
%H A119057 Giovanni Resta, <a href="http://www.numbersaplenty.com/tr/tr029.html">Tridigital Triangular Numbers</a>.
%F A119057 a(n) = A000217(A119058(n)). - _Michel Marcus_, Mar 27 2023
%Y A119057 Cf. A000217, A058428, A119058. See A119033 for a table of cross-references.
%K A119057 nonn,base,more
%O A119057 1,1
%A A119057 _Giovanni Resta_, May 10 2006