def _falling_factorial(x, n):
 val = 1
 for k in range(((x - n) + 1), (x + 1)):
  val *= k
 return val

def _falling_factorial ( x , n ) : val = 1 for k in range ( ( ( x - n ) + 1 ) , ( x + 1 ) ) : val *= k return val
return the factorial of x to the n falling .