FACTDOUBLE

FACTDOUBLE(number)

Returns the double factorial of a positive whole number.

number

The number you want the double factorial of.

REMARKS

* The double factorial is similar to the factorial, except it decrements by 2.
* The double factorial of an even number is n*(n-2)*(n-4)...(4)*(2)
* The double factorial of an odd number is n*(n-2)*(n-4)...(3)*(1)
* The double factorial of 0 is 1.
* 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).
* You can use the FACT function to return the factorial of a positive whole number.
* You can use the MULTINOMIAL function to return the factorial of the sum of values divided by the product of the values.
* For the Microsoft documentation refer to support.microsoft.com

	A	B
1	=FACTDOUBLE(0) = 1	= 0!! = 1
2	=FACTDOUBLE(1) = 1	= 1!! = 1
3	=FACTDOUBLE(2) = 2	= 2!! = 2
4	=FACTDOUBLE(3) = 3	= 3!! = 3*1
5	=FACTDOUBLE(4) = 8	= 4!! = 4*2
6	=FACTDOUBLE(5) = 15	= 5!! = 531
7	=FACTDOUBLE(6) = 48	= 6!! = 642
8	=FACTDOUBLE(7) = 105	= 7!! = 753*1
9	=FACTDOUBLE(4.1) = 8
10	=FACTDOUBLE(4.9) = 8
11	=FACTDOUBLE(-1) = 1
12	=FACTDOUBLE(-2) = #NUM!

1 - What is the double factorial of 0.
2 - What is the double factorial of 1.
3 - What is the double factorial of 2.
4 - What is the double factorial of 3.
5 - What is the double factorial of 4.
6 - What is the double factorial of 5.
7 - What is the double factorial of 6.
8 - What is the double factorial of 7.
9 - What is the double factorial of 4.1. This gets truncated to 4.
10 - What is the double factorial of 4.999. This gets truncated to 4.
11 - What is the double factorial of -1.
12 - What is the double factorial of -2.