Excel Function FACTDOUBLE

FACTDOUBLE(number)

Returns the double factorial of a number.

number

The number you want the double factorial of.

Remarks

* If "number" < 0, then #NUM! is returned.
* If "number" is not numeric, then #VALUE! is returned.
* If "number" is even then, formula used is: n(n-2)(n-4) to (4)(2).
* If "number" is odd then, formula used is: n(n-2)(n-4) to (3)(1).
* In Excel 2010 the accuracy of this function has improved.
* For the Microsoft documentation refer to support.microsoft.com

	A	B
1	=FACTDOUBLE(3) = 3	=3*(3-2) = 3
2	=FACTDOUBLE(4) = 8	=4*(4-2) = 8
3	=FACTDOUBLE(5) = 15	=5(5-2)(5-4) = 15
4	=FACTDOUBLE(6) = 48	=6(6-2)(6-4) = 48
5	=FACTDOUBLE(7) = 105	=7(7-2)(7-4)*(7-6) = 105
6	=FACTDOUBLE(7.9) = 105	=7(7-2)(7-4)*(7-6) = 105
7	=FACTDOUBLE(12) = 46080	=12(12-2)(12-4)(12-6)(12-8)*(12-10) = 46080
8	=FACTDOUBLE(-4) = #NUM!
9	=FACTDOUBLE("some text") = #VALUE!