scipy.special.factorialk

scipy.special.factorialk(n, k, exact=True)

Multifactorial of n of order k, n(!!…!).

This is the multifactorial of n skipping k values. For example,

factorialk(17, 4) = 17!!!! = 17 * 13 * 9 * 5 * 1

In particular, for any integer n, we have

factorialk(n, 1) = factorial(n)

factorialk(n, 2) = factorial2(n)

Parameters:

n : int

Calculate multifactorial. If n < 0, the return value is 0.

k : int

Order of multifactorial.

exact : bool, optional

If exact is set to True, calculate the answer exactly using integer arithmetic.

Returns:

val : int

Multifactorial of n.

Raises:

NotImplementedError

Raises when exact is False

Examples

>>> from scipy.special import factorialk
>>> factorialk(5, 1, exact=True)
120L
>>> factorialk(5, 3, exact=True)
10L