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Excel FACTDOUBLE Function

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.