Computing factorials

[Truman]

Question:
Write a program which can compute the factorial of a given numbers.
The results should be printed in a comma-separated sequence on a single line.

my code:

numb = input("Please add a number: ")
def numb_f(x):
    i = 1
    suma = 1
    while i < int(numb):
        suma =  suma * (i+1)
        i = i + 1
        
print(numb_f(numb))

the output is always "None". Don't know why, please advise.