A double factorial is calculated differently for even and odd numbers.
The double factorial for both zero and -1 are defined as 1.
For numbers less than -1, a double factorial is not defined.
FACTDOUBLE takes just oneargument,number, which should be a positive integer.
Ifnumberis not an integer, the decimal portion ofnumberwill be removed before the factorial is calculated.
For example, =FACT(3) returns 6, equivalent to 3 x 2 x 1.
