The Excel FACTDOUBLE function returns the double factorial of a number. A double factorial is symbolized by two exclamation marks (!!).
Get double factorial of a number
number - A number greater than or equal to -1.
The FACTDOUBLE function returns the double factorial of a number. A double factorial is calculated differently for even and odd numbers. For an even number, n, it's the product of all even integers less than or equal to n and greater than or equal to 2. For an odd number, the double factorial is the product of all odd integers less than or equal to n and greater than or equal to 1. The double factorial for both zero and -1 are defined as 1. For numbers less than -1, a double factorial is not defined.
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