Question 501801
The recursive rule is 


<img src="http://latex.codecogs.com/gif.latex?\huge \dpi{150} a_{n} = \frac{a_{n-1}}{2}" title="\huge \dpi{150} a_{n} = \frac{a_{n-1}}{2}" />



Basically, to find the nth term <img src="http://latex.codecogs.com/gif.latex?\LARGE \inline \dpi{120} a_{n}" title="\LARGE \inline \dpi{120} a_{n}" />, you divide the previous term <img src="http://latex.codecogs.com/gif.latex?\LARGE \inline \dpi{120} a_{n-1}" title="\LARGE \inline \dpi{120} a_{n-1}" /> by 2 (ie you're cutting the previous term in half)



We can see this as 36 jumps to 18 (it cuts in half since 36/2 = 18) and similarly when 18 jumps to 9 (again, 18/2 = 9)