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%I #11 Dec 15 2017 14:28:04
%S 1,3,7,9,15,21,27,31,39,45,63,81,87,93,111,117,127,135,159,183,189,
%T 243,255,261,279,327,333,351,375,381,405,447,471,477,511,543,549,567,
%U 639,729,735,759,765,783,837,975,981,999,1023,1047,1053,1119,1125,1143,1215,1311,1335,1341,1407,1413,1431,1503,1527,1533,1623
%N Increasing sequence generated by these rules: a(1)=1, and if x is in a then 3x and 4x+3 are in a.
%C See A191113.
%H Reinhard Zumkeller, <a href="/A191131/b191131.txt">Table of n, a(n) for n = 1..10000</a>
%t h = 3; i = 0; j = 4; k = 3; f = 1; g = 9;
%t a = Union[Flatten[NestList[{h # + i, j # + k} &, f, g]]] (* A191131 *)
%t b = a/3; c = (a - 3)/4; r = Range[1, 1500];
%t d = Intersection[b, r] (* A191186 *)
%t e = Intersection[c, r] (* A191187 *)
%o (Haskell)
%o import Data.Set (singleton, deleteFindMin, insert)
%o a191131 n = a191131_list !! (n-1)
%o a191131_list = f $ singleton 1
%o where f s = m : (f $ insert (3*m) $ insert (4*m+3) s')
%o where (m, s') = deleteFindMin s
%o -- _Reinhard Zumkeller_, Jun 01 2011
%Y Cf. A191113, A191186, A191187.
%Y Note that A191131, A261524, A261871, and A282572 are very similar and easily confused with each other.
%K nonn
%O 1,2
%A _Clark Kimberling_, May 27 2011
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