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 A119193 #10 Jul 13 2021 21:28:44
%S A119193 2,10,34,109,8189,108989,4470645,32727845,1095073836189,
%T A119193 1091781620649419010
%N A119193 Numbers k such that the k-th triangular number contains only digits {3,5,9}.
%H A119193 G. Resta, <a href="http://www.numbersaplenty.com/tr/tr359.html">Tridigital Triangular Numbers</a>
%Y A119193 Cf. A000217, A119192. See A119034 for a table of cross-references.
%K A119193 nonn,base,more
%O A119193 1,1
%A A119193 _Giovanni Resta_, May 10 2006
%E A119193 a(10) from _Max Alekseyev_, May 21 2011