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 A191110 #10 Sep 30 2019 11:21:56
%S A191110 1,3,5,9,11,15,17,27,29,33,35,45,47,51,53,81,83,87,89,99,101,105,107,
%T A191110 135,137,141,143,153,155,159,161,243,245,249,251,261,263,267,269,297,
%U A191110 299,303,305,315,317,321,323,405,407,411,413,423,425,429,431,459,461,465,467,477,479,483,485,729,731,735,737,747,749,753,755,783
%N A191110 Increasing sequence generated by these rules: a(1)=1, and if x is in a then 3x and 3x+2 are in a.
%C A191110 See discussions at A190803, A191106. A191110 has closure properties: the positive integers in (A191110)/3 form A191110, and likewise for (-2+A191110).
%H A191110 Ivan Neretin, <a href="/A191110/b191110.txt">Table of n, a(n) for n = 1..10000</a>
%t A191110 h = 3; i = 0; j = 3; k = 2; f = 1; g = 7;
%t A191110 a = Union[Flatten[NestList[{h # + i, j # + k} &, f, g]]] (* A191110 *)
%t A191110 b = a/3; c = (a - 2)/3; r = Range[0, 900];
%t A191110 d = Intersection[b, r] (* A191110 closure property *)
%t A191110 e = Intersection[c, r] (* A191110 closure property *)
%t A191110 Flatten[Nest[{#,3#,3#+2}&/@#&,{1},6]]//Union (* _Harvey P. Dale_, Sep 30 2019 *)
%Y A191110 Cf. A190803, A191106.
%K A191110 nonn
%O A191110 1,2
%A A191110 _Clark Kimberling_, May 26 2011