**Using the Excel FACTDOUBLE Function**

## Summary

The Excel FACTDOUBLE function is used to return the double factorial of a number. The double factorial is symbolized using double exclamation marks. For example, 8!!.See the FACT function if you need the factorial of a number.

## Syntax

=FACTDOUBLE (number)## Syntax Breakdown

**Number**Required. The number for which you want to find the double factorial. If it is not an integer, it will be truncated.

## Usage Notes

The FACTDOUBLE function returns the double factorial of a given non-negative number. The function returns the #NUM! error if a negative number is entered.If number is non-numeric the function will return the #VALUE! error.

**Calculation**The double factorial is calculated differently for even and odd numbers. If the number, n, is

__even__, then the double factorial is the product of all even integers less than or equal to n and greater than or equal to 2. For example, the double factorial of 6 would be found by 6 * 4 * 2 = 48.

If the number, n, is odd, then the double factorial is the product of all odd integers less than or equal to n and greater than or equal to 1. For example, the double factorial of 9 would be found by 9 * 7 * 5 * 3 * 1 = 945.

A double factorial is not defined for numbers less than -1. For 0 (zero) and 1, the double factorial is 1.