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N! = N * (N-1) * (N-2) * ... * 1. The factorial of zero is one because it is an {empty product}. Factorial can be defined {recursively} as 0! = 1 N! = N * (N-1)! , N > 0 The {gamma function} is the equivalent for real numbers. (2005-01-07) スポンサード リンク
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