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 A119144 #10 Mar 24 2023 04:24:16
%S A119144 1,6,66,91,666,961191,996166,1191196,96111966961,99119996661,
%T A119144 16161696119661,196999111911966,661969169911666,11961669169169616,
%U A119144 19961691661699161,991961666199161911,6116119911196616916,16961161696691611916961,911666691991111199916696
%N A119144 Triangular numbers composed of digits {1,6,9}.
%H A119144 Giovanni Resta, <a href="http://www.numbersaplenty.com/tr/tr169.html">Tridigital Triangular Numbers</a>
%F A119144 a(n) = A000217(A119145(n)). - _Michel Marcus_, Mar 24 2023
%Y A119144 Cf. A000217, A053911, A119145. See A119033 for a table of cross-references.
%K A119144 nonn,base
%O A119144 1,2
%A A119144 _Giovanni Resta_, May 10 2006
%E A119144 a(18)-a(19) from _Tyler Busby_, Mar 24 2023