This is a tool that calculates the number of permutations of n distinct objects taken r at a time (i.e. when the order matters).

For this calculation, it is necessary to supply the following information:

- The number of objects to choose from (n).
- The number of objects taken at a time (r).
- Whether repetition is allowed or not, i.e. whether an object can be used more than once in a permutation or not (e.g. is AAA a valid permutation from the letters ABC?).

Associated tool link: http://www.coggit.com/tools/number_of_permutations.html