OFFSET
1,1
REFERENCES
J. C. Lagarias, ed., The Ultimate Challenge: The 3x+1 Problem, Amer. Math. Soc., 2010; see page 270.
LINKS
Reinhard Zumkeller, Table of n, a(n) for n = 1..10000
J. C. Lagarias, The 3x+1 problem and its generalizations, Amer. Math. Monthly, 92 (1985), 3-23.
Index entries for linear recurrences with constant coefficients, signature (0, 0, 0, 0, 1).
FORMULA
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.
MATHEMATICA
Table[{4, 5, 7, 9, 6}, {21}] // Flatten (* Jean-François Alcover, Jun 10 2013 *)
LinearRecurrence[{0, 0, 0, 0, 1}, {4, 5, 7, 9, 6}, 105] (* Ray Chandler, Sep 03 2015 *)
PROG
(Haskell)
a094328 n = a094328_list !! (n-1)
a094328_list = iterate a006369 4 -- Reinhard Zumkeller, Dec 31 2011
(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
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
N. J. A. Sloane, Jun 04 2004
STATUS
approved