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 A191287 #7 Nov 17 2016 12:14:03
%S A191287 1,3,4,6,9,12,13,18,19,27,28,36,39,40,42,54,57,58,60,63,81,84,85,87,
%T A191287 90,94,108,117,120,121,126,127,130,135,141,162,171,174,175,180,181,
%U A191287 189,190,195,202,211,243,252,255,256,261,262,270,271,282,283,285,292,303,316,324,351,360,363,364,378,381,382,384,390,391,393,405
%N A191287 Increasing sequence generated by these rules: a(1)=1, and if x is in a then floor(3x/2) and 3x are in a.
%C A191287 See A191203.
%H A191287 Ivan Neretin, <a href="/A191287/b191287.txt">Table of n, a(n) for n = 1..10000</a>
%e A191287 1 -> 3 -> 4,9 -> 6,12,13,27 ->
%t A191287 g=15; Union[Flatten[NestList[{Floor[3#/2],3#} &, 1, g]]]
%t A191287 (* A191287; use g>14 to get all of first 60 terms *)
%Y A191287 Cf. A191203.
%K A191287 nonn
%O A191287 1,2
%A A191287 _Clark Kimberling_, May 29 2011