Calculating a Bijective Function: f(N0)

[blob84]

Hi, i have this function $f : x \in Q \rightarrow (5x-7)/6$
the function is bijective now i need to calculate:
$f(N0)$
i get :
$f(0)=-7/6$, $f(1)=-1/3$, $f(2)=1/2$, $f(3)=4/3$, etc...
I need to generalize the set that include the image of $f(N0)$,
but i don't know what could be.

 

[micromass]

Let's not simplify the fraction. Then the denominator will always be 6. What can the numerator be?