Returns the double factorial of the given number.

**Sample Usage**

FACTDOUBLE(5)

FACTDOUBLE(C5)

**Syntax**

FACTDOUBLE(number)

- number - The number for which the double factorial is to be computed.

**Examples**

FACTDOUBLE(5) returns the number 15.

FACTDOUBLE(C5) returns the double factorial of the number contained in C5.

**Notes**

- Decimal inputs will be truncated.
- If is number is odd, double factorial is calculated as follows:
- n!! = n*(n-2)*(n-4)...(3)(1)

- If is number is even, double factorial is calculated as follows:
- n!! = n*(n-2)*(n-4)...(4)(2)