Permutations

Hi

I have three possible letters, let say they are A,B and C. I am looking for an easy solution to create from five letter to fiveteen letter list of permutations from these.

The lenght of the permutation needs to be attached to a cell. Lets say a cell has number five and then the five letter permutations are created and if the cell number gets changed also the lenght of the permutation gets changed.

Thanks for the help.