使用Python來計算m階下降階乘

Question

下降階乘：https://en.wikipedia.org/wiki/Falling_and_rising_factorials

如何使用Python來計算呢？我嘗試

def factorial(gamma, m): 
    prod = 1 
    for i in range(m): 
     prod *= (1-gamma-i) 

Answer 1

你忘了return語句。

def factorial(gamma, m): 
    prod = 1 
    for i in range(m): 
     prod *= (1-gamma-i) 
    return prod 

1 - γ= X

factorial(-4, 1) = 120