Statistics and Probability Dictionary

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Factorial

In general, n objects can be arranged in n(n - 1)(n - 2) ... (3)(2)(1) ways. This product is represented by the symbol n!, which is called n factorial. By convention, 0! = 1.

Thus, 0! = 1; 2! = (2)(1) = 2; 3! = (3)(2)(1) = 6; 4! = (4)(3)(2)(1) = 24; 5! = (5)(4)(3)(2)(1) = 120; and so on.

See also:   Rules of Counting | Event Counter