FACTDOUBLE

FACTDOUBLE(number)

Returns the double factorial of a positive whole number.

numberThe 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
* For the Google documentation refer to support.google.com

 AB
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!! = 5*3*1
7=FACTDOUBLE(6) = 48 = 6!! = 6*4*2
8=FACTDOUBLE(7) = 105 = 7!! = 7*5*3*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.

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