In math, we write a permutation like this:
In plain language, this represents the number of possible permutations when you choose elements from a collection of elements. The subscript indicates that the expression represents a permutation where order matters. See the combination notation for when order does not matter.
In general, to express choose permutations we write:
To calculate the number of permutations see this formula.
The number of combinations of r items chosen from n total items is written as the two values stacked inside parentheses with a subscript c.