Create a function that tests if a number is the exact upper bound of the factorial of n. If so, return an array of the exact factorial bound and n, or otherwise, an empty array.

Examples

isExact(6) ➞ [6, 3]

isExact(24) ➞ [24, 4]

isExact(125) ➞ []

isExact(720) ➞ [720, 6]

isExact(1024) ➞ []

isExact(40320) ➞ [40320, 8]

Notes

There will be no exceptions to handle, all inputs are positive integers.