Permutations
Arrangement of r objects from a set of n objects, where \(r \leq n\).
E.g. for “abc” we have abc acb bac bca cab cba
Formula
Base
nPr = n * (n - 1) * (n - 2) * … * (n - (r - 1)) = n!/(n-r)!
Duplicates
e.g. abccdd
nPr / 2!2!
Circle
n! / n = (n - 1)!