Number of all possible orderings of n distinct elements.
Ordering of n elements where items repeat k1, k2... times.
Selecting k elements from n where order matters and items cannot repeat.
Selecting k elements from n where order matters and items can repeat.
Selecting k elements from n where order does not matter and items cannot repeat.
Selecting k elements from n where order does not matter and items can repeat.
P(5) = 5!