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 A191290 #7 Nov 17 2016 12:13:54
%S A191290 1,3,6,7,13,15,21,27,28,31,43,55,57,63,87,91,111,115,120,127,175,183,
%T A191290 223,231,241,255,351,367,378,406,447,463,483,496,511,703,735,757,813,
%U A191290 895,927,946,967,993,1023,1407,1471,1515,1540,1627,1653,1791,1855,1893,1935,1987,2016,2047,2815,2943,3031,3081,3255,3307,3583
%N A191290 Increasing sequence generated by these rules: a(1)=1, and if x is in a then 2x+1 and x(x+1)/2 are in a.
%C A191290 See A191203.
%H A191290 Ivan Neretin, <a href="/A191290/b191290.txt">Table of n, a(n) for n = 1..10000</a>
%e A191290 1 -> 3 -> 6,7 -> 13,15,21,28 ->
%t A191290 g=11; Union[Flatten[NestList[{1+2#, (#^2+#)/2} &, 1, g]]]
%t A191290 (* A191290; use g>9 to get all of first 60 terms *)
%Y A191290 Cf. A191203.
%K A191290 nonn
%O A191290 1,2
%A A191290 _Clark Kimberling_, May 29 2011