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A191128 Increasing sequence generated by these rules: a(1)=1, and if x is in a then 3x and 4x-1 are in a. 4

%I #8 Jul 13 2013 12:04:10

%S 1,3,9,11,27,33,35,43,81,99,105,107,129,131,139,171,243,297,315,321,

%T 323,387,393,395,417,419,427,513,515,523,555,683,729,891,945,963,969,

%U 971,1161,1179,1185,1187,1251,1257,1259,1281,1283,1291,1539,1545,1547,1569,1571,1579,1665,1667,1675,1707,2049,2051,2059,2091,2187

%N Increasing sequence generated by these rules: a(1)=1, and if x is in a then 3x and 4x-1 are in a.

%C See A191113.

%H Reinhard Zumkeller, <a href="/A191128/b191128.txt">Table of n, a(n) for n = 1..10000</a>

%t h = 3; i = 0; j = 4; k = -1; f = 1; g = 9;

%t a = Union[Flatten[NestList[{h # + i, j # + k} &, f, g]]] (* A191128 *)

%t b = a/3; c = (a + 1)/4; r = Range[1, 1500];

%t d = Intersection[b, r] (* A191180 *)

%t e = Intersection[c, r] (* A191181 *)

%t m = (a + 1)/2 (* divisibility property *)

%o (Haskell)

%o import Data.Set (singleton, deleteFindMin, insert)

%o a191128 n = a191128_list !! (n-1)

%o a191128_list = f $ singleton 1

%o where f s = m : (f $ insert (3*m) $ insert (4*m-1) s')

%o where (m, s') = deleteFindMin s

%o -- _Reinhard Zumkeller_, Jun 01 2011

%Y Cf. A191113, A191180, A191181.

%K nonn

%O 1,2

%A _Clark Kimberling_, May 27 2011

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Last modified March 28 20:05 EDT 2024. Contains 371254 sequences. (Running on oeis4.)