Generate a unique N letters word sequence (by using relationship between Factoradic base system and Lexicographic Permutation Order of a String)

Lets say that you want to generate a unique 3 letters code sequence to be used as a primary key for some data recodes. Also let assume that you are allowed to use alphanumeric characters. For example:

• ABC ->  Data Recored 1
• CBA -> Data Recored 2
• Z1T  -> Data Recored 3
• R39  -> Data Recored 4
• etc ..