Possible Duplicate: Prove 0! = 1 0! = 1 from first principles Why does 0! = 1 0! = 1? All I know of factorial is that x! x! is equal to the product of all the numbers that come before it. The product of 0 and anything is 0 0, and seems like it would be reasonable to assume that 0! = 0 0! = 0. I’m perplexed as to why I have to account for this condition in my factorial function (Trying to learn …
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