Ah, an existance-and-uniqueness proof. I'll state it: The "factoralary" representation of every natural number n exists and is unique. It would be tough to do a whole proof here in plain text, but my gut just tells me to do a proof by contradiction for the uniqueness part. That is, assume that a number n has 2 distinct representations in factoralary form, and then show some kind of contradiction. The existance part seems kind of simple...every time you add 1 to a number, you increase the 1! digit by 1. If that causes overflow, you 'carry' it to the 2!, and make the 1! digit 0. If there's overflow in the 2! place, carry THAT one to the 3! place, making the 2! zero. A formal proof of this kind of smells like it would best be served by induction. I swear I saw a problem like this. Perhaps "The Art of Problem Solving" - volume I or II? It was how I learned all my geeky number theory for high school math competitions back in the day.... EDIT - I found a wikipedia article on this base...it sort of skirts around your question, but it does touch on it. It also adds a '0' to every digit, and has a 0!s place. EDIT of EDIT - DOH. I was beaten to the punch. :(
BY definition, x^n is x multiplied by itself n times
and
x^(-n) is 1 over x^n
According to the rules of of exponential multiplication/division, when you multiply 2 exponential numbers together (when they have the same base), you ADD the exponents. Thus x^m * x ^ n = x^(m + n)
Likewise, when you divide, you subtract the exponents
If you have x^n * x^(-n), this is the same as x^n/x^n which is obviously 1. Therefore, x^n * x^-n must equal 1. But according to the rules of exponential multiplication above, x^n * x^-n =
x^(n-n) = x^0