If n is a positive integer and n = r^k, where r and k are positive integers, then iperfpow(n) returns r.  If the second argument, 'p', is specified in the calling sequence, it is assigned the value k.

It is an error for n to evaluate to a numeric which is not a positive integer.

This function returns FAIL if it is not able to establish that n is a perfect power of an integer.

In all other cases, the function returns unevaluated.