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A191203
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Increasing sequence generated by these rules: a(1)=1, and if x is in a then 2x and 1+x^2 are in a.
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13
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1, 2, 4, 5, 8, 10, 16, 17, 20, 26, 32, 34, 40, 52, 64, 65, 68, 80, 101, 104, 128, 130, 136, 160, 202, 208, 256, 257, 260, 272, 290, 320, 401, 404, 416, 512, 514, 520, 544, 580, 640, 677, 802, 808, 832, 1024, 1025, 1028, 1040, 1088, 1157, 1160, 1280, 1354, 1601, 1604, 1616, 1664, 2048, 2050, 2056, 2080, 2176, 2314, 2320, 2560
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OFFSET
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1,2
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COMMENTS
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The method generalizes: a finite set F={f} of functions f:N->N and finite set G of numbers generate a set S by these rules: (1) every element of G is in S, and (2) if x is in S then f(x) is in S for every f in F. The sequence a results by taking the numbers in S in increasing order.
For A191203 and other such sequences, the depth g for the NestList in the Mathematica program must be large enough to generate as many terms as required by the user. For example, the rules 2x and 1+x^2, starting with x=1, successively generate set of numbers whose minima are powers of 2: 1->2->4-> ... 2^g -> ....
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LINKS
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EXAMPLE
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1 -> 2 -> 4,5 -> 8,10,17,26 ->
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MATHEMATICA
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g = 12; Union[Flatten[NestList[{2 #, 1 + #^2} &, 1, g]]]
(* A191203; use g>11 to get all terms up to 4096 *)
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PROG
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(Haskell)
import Data.Set (singleton, deleteFindMin, insert)
a191203 n = a191203_list !! (n-1)
a191203_list = f $ singleton 1 where
f s = m : f (insert (2 * m) $ insert (m ^ 2 + 1) s')
where (m, s') = deleteFindMin s
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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