The Excel Permut and Permutationa functions both calculate the number of permutations of a selection of objects from a set.
However, the two functions differ in that the Permut function does not count repetitions whereas the Permutationa function does count repetitions.
For example, in a set of 3 objects, a, b, c, how many permutations of 2 objects are there?
The Excel Permutationa function calculates the number of permutations, with repetitions, of a specified number of objects from a set.
The syntax of the function is:
Where the function arguments are:
number    The total number of objects in the set (must be ≥ 0). 
number_chosen    The number of objects selected from the set (must be ≥ 0). 
Note that, if any of the arguments are supplied as decimal values, they are truncated to integers by the permutationa function.
In the spreadsheet below, the Excel Permutationa function is used to calculate the number of permutations (with repetitions) of six objects, selected from different sized sets.
Formulas:

Results:

For further details and examples of the Excel Permutationa function, see the Microsoft Office website.
If you get an error from the Excel Permutationa Function, this is likely to be one of the following:
#NUM!   
Occurs if either:

#VALUE!    Occurs one or both of the supplied arguments are nonnumeric. 