FactDouble-func
This function is used to calculate the double factorial of a non-negative integer n, denoted by:
Please note that, to avoid overflow, the biggest integer can be specified is 299, if bigger than 299, this function will return missing value directly.
double FactDouble(int n)
n
Return the double factorial of the specified number.
factdouble(5) = ; // 5*3*1=15 factdouble(6) = ; // 6*4*2=48 factdouble(0) = ; // 1 factdouble(1) = ; // 1
Fact