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 A119111 #11 Apr 06 2023 20:00:30
%S A119111 1,3,1431,33411,331441131,1444343131,13113334431,31444341333441,
%T A119111 111413314441131,444334341314331,11114441143333344141,
%U A119111 331341331134344133331,4443314433131433343331311434133434431331
%N A119111 Triangular numbers composed of digits {1,3,4}.
%C A119111 a(14) > 10^41. - _Tyler Busby_, Mar 27 2023
%H A119111 Giovanni Resta, <a href="http://www.numbersaplenty.com/tr/tr134.html">Tridigital Triangular Numbers</a>.
%F A119111 a(n) = A000217(A119112(n)). - _Tyler Busby_, Mar 27 2023
%Y A119111 Cf. A000217, A053891, A119112. See A119033 for a table of cross-references.
%K A119111 nonn,base,more
%O A119111 1,2
%A A119111 _Giovanni Resta_, May 10 2006
%E A119111 a(13) from _Tyler Busby_, Mar 27 2023