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 A119112 #14 Mar 31 2023 00:50:12
%S A119112 1,2,53,258,25746,53746,161946,7930238,14927378,29810546,4714751561,
%T A119112 25742623453,94268917816334704578
%N A119112 Numbers k such that the k-th triangular number contains only digits {1,3,4}.
%H A119112 Giovanni Resta, <a href="http://www.numbersaplenty.com/tr/tr134.html">Tridigital Triangular Numbers</a>.
%t A119112 (Sqrt[8#+1]-1)/2&/@Table[Select[FromDigits/@Tuples[{1,3,4},n],OddQ[ Sqrt[ 8#+1]]&],{n,21}]//Flatten (* _Harvey P. Dale_, Jul 09 2017 *)
%Y A119112 Cf. A000217, A119111. See A119034 for a table of cross-references.
%K A119112 nonn,base,more
%O A119112 1,2
%A A119112 _Giovanni Resta_, May 10 2006
%E A119112 a(13) from _Tyler Busby_, Mar 30 2023