Definition:Permutation/Ordered Selection/Notation

Definition
The number of $r$-permutations from a set of cardinality $n$ is denoted variously:
 * $P_{n r}$
 * ${}^r P_n$
 * ${}_r P_n$
 * ${}_n P_r$ (extra confusingly)

There is little consistency in the literature).

On the notation of choice is ${}^r P_n$.