I'm sure you're familiar with factorials – that is, the product of an integer and all the integers below it. 
For example, `5! = 120`, as `5 * 4 * 3 * 2 * 1 = 120`
Your challenge is to create a function that takes any number and returns the number that it is a factorial of. So, if your function receives `120`, it should return `"5!"` (as a string).
Of course, not every number is a factorial of another. In this case, your function would return `"None"` (as a string).
### Examples
* `120` will return `"5!"`
* `24` will return `"4!"`
* `150` will return `"None"`
def reverse_factorial(num):
    i = 1
    while 1:
        num, m = num / i, num % i
        if m != 0: return 'None'
        if num == 1: return str(i)+'!'
        i += 1

def reverse_factorial(num):
    i = 1
    while 1:
        num, m = num / i, num % i
        if m != 0: return 'None'
        if num == 1: return str(i)+'!'
        i += 1
