$\mathrm {\left\lfloor\mathbf{r} \cdot{ }^{n} \mathbf{P}_{\mathrm{r}}=?\right.}$

$\mathrm { \frac{\lfloor {}n}{\lfloor {(n-r)}}}$

$\mathrm { \frac{\lfloor {}n}{ \lfloor {r} {~}\lfloor {(n-r)}}}$

$\mathrm { \frac{\lfloor {r}{~} \lfloor{n}}{\lfloor {(n-r)}}}$

$\mathrm { \frac{\lfloor {(n-r)}}{\lfloor {r}}}$