In the context of counting problems, Permutations is the arrangements where the order is important and repetitions or recurrence is not allowed. The number of permutations of n distinct points taken r at a time is written as nPr. Because the number of objects is being arranged cannot exceed total number available. There are n! (n factorial) permutations of n symbols. A r-permutation of n symbols is a permutation of r of them. There are n!/(n - r)! different r-permutations of n symbols. A permutations represented by nPr
nPr = n!/(n - r)!