Write a recursive method called permut that accepts two integers n and r as parameters and returns the number of unique permutations of r items from a group of n items. For given values of n and r, this value P(n, r) can be computed as follows:
For example, permut(7, 4) should return 840. It may be helpful to note that permut(6, 3) returns 120, or 840 / 7.