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A002517
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Earliest sequence with a(a(n))=3n.
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10
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0, 2, 3, 6, 5, 12, 9, 8, 21, 18, 11, 30, 15, 14, 39, 36, 17, 48, 27, 20, 57, 24, 23, 66, 63, 26, 75, 54, 29, 84, 33, 32, 93, 90, 35, 102, 45, 38, 111, 42, 41, 120, 117, 44, 129, 108, 47, 138, 51, 50, 147, 144, 53, 156, 81, 56, 165, 60, 59, 174, 171, 62, 183, 72, 65, 192
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listen;
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OFFSET
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0,2
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COMMENTS
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LINKS
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FORMULA
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a(3n)=3*a(n), a(3n+1)=3n+2, a(3n+2)=9n+3
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MATHEMATICA
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a[n_] := a[n] = Which[ Mod[n, 3] == 0, 3*a[n/3], Mod[n, 3] == 1, n+1, True, 3*(n-1)]; Table[a[n], {n, 0, 65}] (* Jean-François Alcover, Sep 24 2012 *)
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PROG
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(Haskell)
import Data.List (transpose)
a002517 n = a002517_list !! n
a002517_list = 0 : concat
(transpose [[2, 5 ..], [3, 12 ..], map (* 3) $ tail a002517_list])
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CROSSREFS
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KEYWORD
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nonn,nice,easy
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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