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 A119192 #12 Mar 29 2023 15:37:56
%S A119192 3,55,595,5995,33533955,5939355555,9993335593335,535555935535935,
%T A119192 599593353353393939939955,595993553593935939553359535599399555
%N A119192 Triangular numbers composed of digits {3,5,9}.
%C A119192 a(11) > 10^39. - _Tyler Busby_, Mar 29 2023
%H A119192 Giovanni Resta, <a href="http://www.numbersaplenty.com/tr/tr359.html">Tridigital Triangular Numbers</a>.
%F A119192 a(n) = A000217(A119193(n)).
%Y A119192 Cf. A000217, A119193. See A119033 for a table of cross-references.
%K A119192 nonn,base,more
%O A119192 1,1
%A A119192 _Giovanni Resta_, May 10 2006
%E A119192 a(10) from _Max Alekseyev_, May 21 2011