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 A119130 #10 Mar 31 2023 15:35:59
%S A119130 1,91,49141,144991,94414411,941194191,1194944941,491919414441,
%T A119130 9999119991411411,4149449911949149941,11144994144991949991,
%U A119130 191444491991911949911,144949944191119411441191,9449441991199141999494149499499111914141
%N A119130 Triangular numbers composed of digits {1,4,9}.
%H A119130 Giovanni Resta, <a href="http://www.numbersaplenty.com/tr/tr149.html">Tridigital Triangular Numbers</a>.
%F A119130 a(n) = A000217(A119131(n)). - _Tyler Busby_, Mar 31 2023
%Y A119130 Cf. A000217, A006716, A119131. See A119033 for a table of cross-references.
%K A119130 nonn,base
%O A119130 1,2
%A A119130 _Giovanni Resta_, May 10 2006
%E A119130 a(14) from _Max Alekseyev_, Aug 15 2013