Excel FACTDOUBLE Function
Summary
The Excel FACTDOUBLE function returns the double factorial of a number. A double factorial is symbolized by two exclamation marks (!!).
Purpose
Get double factorial of a number
Return value
Calculated doublefactorial
Syntax
=FACTDOUBLE (number)
Arguments
- number - A number greater than or equal to -1.
Usage notes
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.
For example, the double factorial of 8 is:
=FACTDOUBLE(8) =8*6*4*2 =384
For example, the double factorial of 7 is:
=FACTDOUBLE(7) =7*5*3*1 =105
Notes:
- The number cannot be negative or FACTDOUBLE will return the #NUM error.
- If the number is not an integer it will be truncated to an integer, then solved.
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