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!! = special.gamma(n/2+1)*2**((m+1)/2)/sqrt(pi) n odd = 2**(n/2) * (n/2)! n even
- Parameters
- nint or array_like
Calculate
n!!
. Arrays are only supported with exact set to False. 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