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 A119077 #10 Apr 06 2023 20:01:20
%S A119077 990,4009490400090,990440044904409490,9900404040400404004090
%N A119077 Triangular numbers composed of digits {0,4,9}.
%C A119077 a(5) > 10^40. - _Tyler Busby_, Mar 28 2023
%H A119077 Giovanni Resta, <a href="http://www.numbersaplenty.com/tr/tr049.html">Tridigital Triangular Numbers</a>.
%F A119077 a(n) = A000217(A119078(n)). - _Tyler Busby_, Mar 28 2023
%Y A119077 Cf. A000217, A058444, A119078. See A119033 for a table of cross-references.
%K A119077 nonn,base,more
%O A119077 1,1
%A A119077 _Giovanni Resta_, May 10 2006