OFFSET
1,1
COMMENTS
The 5x+1 map sends x to x/2 if x is even, x/3 if x is odd and divisible by 3, otherwise 5x+1.
LINKS
FORMULA
From Chai Wah Wu, Mar 04 2018: (Start)
a(n) = 2*a(n-6) - a(n-12) for n > 12.
G.f.: x*(4*x^10 + x^9 + x^8 + 2*x^7 + 24*x^6 + 3*x^5 + 26*x^4 + 2*x^3 + x^2 + x + 6)/(x^12 - 2*x^6 + 1). (End)
MATHEMATICA
Table[If[EvenQ[n], n/2, If[Mod[n, 3] == 0, n/3, 5*n + 1]], {n, 1, 80}] (* Stefan Steinerberger, Feb 16 2008 *)
Table[Which[EvenQ[n], n/2, Divisible[n, 3], n/3, True, 5n+1], {n, 70}] (* Harvey P. Dale, Jul 08 2018 *)
PROG
(PARI) a(n)=if(n%2, if(n%3, 5*n+1, n/3), n/2) \\ Charles R Greathouse IV, Sep 02 2015
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
N. J. A. Sloane, Nov 27 2007
EXTENSIONS
More terms from Stefan Steinerberger, Feb 16 2008
Comment clarified by Chai Wah Wu, Mar 04 2018
STATUS
approved