code: def 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)
      120
      >>> factorialk(5, 3, exact=True)
      10
  
      """
      if exact:
          if n < 1 - k:
              return 0
          if n <= 0:
              return 1
          val = 1
          for j in range(n, 0, -k):
              val = val * j
          return val
      else:
          raise NotImplementedError
  
imports: import operator
  import numpy
  import math
  from numpy import pi, asarray, floor, isscalar, iscomplex, real, imag, sqrt, where, mgrid, sin, place, issubdtype, extract, inexact, nan, zeros, sinc
  from .None import _ufuncs
  from ._ufuncs import mathieu_a, mathieu_b, iv, jv, gamma, psi, hankel1, hankel2, yv, kv, ndtri, poch, binom, hyp0f1
  from .None import specfun
  from .None import orthogonal
  from ._comb import _comb_int
label_desc: Use image node_id 58 for calling a global function with example usage: factorialk(n, k, exact) and returns: val, int, int