permutation

In mathematics, a specified arrangement of a group of objects.

It is the arrangement of a distinct objects taken b at a time in all possible orders. It is given by a!/(a − b)!, where ‘!’ stands for factorial. For example, the number of permutations of four letters taken from any group of six different letters is 6!/2! = (1 × 2 × 3 × 4 × 5 × 6)/(1 × 2) = 360. The theoretical number of four-letter ‘words’ that can be made from an alphabet of 26 letters is 26!/22! = 358,800.