### Navigation

- index
- modules |
- modules |
- next |
- previous |
- SciPy v0.12 Reference Guide (DRAFT) »
- Miscellaneous routines (`scipy.misc`) »

# scipy.misc.factorial2

`scipy.misc.``factorial2`(n, exact=False)

  Double factorial.

  This is the factorial with every second value skipped, i.e., `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 : | n : int or array_like Calculate `n!!`. Arrays are only supported with exact set to False. If `n < 0`, the return value is 0. exact : bool, 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 : | nff : float or int Double factorial of n, as an int or a float depending on exact.

  Examples

      >>> factorial2(7, exact=False)
      array(105.00000000000001)
      >>> factorial2(7, exact=True)
      105L

### Navigation

- index
- modules |
- modules |
- next |
- previous |
- SciPy v0.12 Reference Guide (DRAFT) »
- Miscellaneous routines (`scipy.misc`) »