As far as I can tell for the equation n!/n^2=x or n-1!/n=x, if x is a natural number then it seems n is composite. If x is a non-natural number then it is prime (excluding 4). I am aware that this is not very practical since I am using factorials and the numbers get very large. But it still seems interesting non the less. As of now I can only test up to n=86. Is there a easier way to check very large numbers? A better on line calculator perhaps? Or is all this something already known and/or disproving? I also noticed that the remainder left over from each prime number increases in value from .5- to .999999..... Since these remainders are generated by primes they seem to grow in prime proportions.