Finding how many numbers are divisible by a prime number I'm trying to figure out how I can find out how many numbers are divisible by a certain prime (eg 3) in a certain range, eg 0-10000. I think it has something to do with permutations, but I'm not really sure and kinda stuck.
Could you please point me in the right direction or so?

For your given range there are $1+\left\lfloor \cfrac{10000}{3} \right\rfloor=1+3333=3334$ numbers divisible by $3$. This count includes the end-points of your range ($0$ and $10000$).
The notation $\lfloor x \rfloor$ (known as ‘the floor function’) denotes the largest integer less than or equal to $x \in \mathbb{R}$. Examples include $\lfloor7\rfloor$ = $7$, $\lfloor2.5\rfloor$ = $2$, $\lfloor\pi\rfloor$= $3$ and  $\lfloor−2.5\rfloor$ = $-3$.
