scipy.special.factorial2#
- scipy.special.factorial2(n, exact=False)[source]#
Double factorial.
This is the factorial with every second value skipped. E.g.,
7!! = 7 * 5 * 3 * 1
. It can be approximated numerically as:n!! = 2 ** (n / 2) * gamma(n / 2 + 1) * sqrt(2 / pi) n odd = 2 ** (n / 2) * gamma(n / 2 + 1) n even = 2 ** (n / 2) * (n / 2)! n even
- Parameters:
- nint or array_like
Calculate
n!!
. Ifn < 0
, the return value is 0.- exactbool, optional
The result can be approximated rapidly using the gamma-formula above (default). If exact is set to True, calculate the answer exactly using integer arithmetic.
- Returns:
- nfffloat or int
Double factorial of n, as an int or a float depending on exact.
Examples
>>> from scipy.special import factorial2 >>> factorial2(7, exact=False) array(105.00000000000001) >>> factorial2(7, exact=True) 105