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A094328
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Iterate the map in A006369 starting at 4.
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21
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4, 5, 7, 9, 6, 4, 5, 7, 9, 6, 4, 5, 7, 9, 6, 4, 5, 7, 9, 6, 4, 5, 7, 9, 6, 4, 5, 7, 9, 6, 4, 5, 7, 9, 6, 4, 5, 7, 9, 6, 4, 5, 7, 9, 6, 4, 5, 7, 9, 6, 4, 5, 7, 9, 6, 4, 5, 7, 9, 6, 4, 5, 7, 9, 6, 4, 5, 7, 9, 6, 4, 5, 7, 9, 6, 4, 5, 7, 9, 6, 4, 5, 7, 9, 6, 4, 5, 7, 9, 6, 4, 5, 7, 9, 6, 4, 5, 7, 9, 6, 4, 5, 7, 9, 6
(list;
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refs;
listen;
history;
text;
internal format)
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OFFSET
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1,1
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REFERENCES
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J. C. Lagarias, ed., The Ultimate Challenge: The 3x+1 Problem, Amer. Math. Soc., 2010; see page 270.
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LINKS
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FORMULA
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The map is: n -> if n mod 3 = 0 then 2*n/3 elif n mod 3 = 1 then (4*n-1)/3 else (4*n+1)/3.
Periodic with period length 5.
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MATHEMATICA
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LinearRecurrence[{0, 0, 0, 0, 1}, {4, 5, 7, 9, 6}, 105] (* Ray Chandler, Sep 03 2015 *)
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PROG
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(Haskell)
a094328 n = a094328_list !! (n-1)
(PARI) a(n)=([0, 1, 0, 0, 0; 0, 0, 1, 0, 0; 0, 0, 0, 1, 0; 0, 0, 0, 0, 1; 1, 0, 0, 0, 0]^(n-1)*[4; 5; 7; 9; 6])[1, 1] \\ Charles R Greathouse IV, Oct 18 2022
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CROSSREFS
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KEYWORD
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nonn,easy
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AUTHOR
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STATUS
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approved
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