Definition:Permutation/Ordered Selection/Notation

Definition
The number of $r$-permutations from a set of cardinality $n$ is denoted variously:
 * ${}_n P_r$
 * ${P_n}^r$
 * $p_{n r}$
 * ${}^n P_r$

There is little consistency in the literature).

On the notation of choice is ${}^n P_r$.