`scipy.special._basic:_range_prod`

Signature

def _range_prod(lo, hi, k = 1)

Product of a range of numbers spaced k apart (from hi).

For k=1, this returns the product of lo * (lo+1) * (lo+2) * ... * (hi-2) * (hi-1) * hi = hi! / (lo-1)!

For k>1, it correspond to taking only every k'th number when counting down from hi - e.g. 18!!!! = _range_prod(1, 18, 4).

Breaks into smaller products first for speed: _range_prod(2, 9) = ((2*3)*(4*5))*((6*7)*(8*9))