Python Program to Find the Factorial of a Number

Ankur Ranpariya
31 Mar, 2022

In this article, we will learn to find the factorial of a number using python program.

What is factorial?

In mathematics, the factorial of a non-negative integer n is the product of all positive integers less than or equal to n. The factorial of n also equals the product of n with the next smaller factorial.

n! = n x (n-1) x (n-2) x (n-3) x ....x 3 x 2 x 1

For example,

4! = 4 x 3 x 2 x 1 = 24

Now, using python we find the factorial of any number using 3 methods. 

Using loops 

Using the loop we find the factorial of the number. Factorial of number is equal to the product of 1 to that number.

For example,

5! = 1 x 2 x 3 x 4 x 5 = 120

Program

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# python program to find the factorial of number using for loop
# take any number assigned it in variable named n
n = 5

# if n is negative integer then the factorial is not exits
if n<0:
    print("Factorial of negative number not possible")

# factorial of 0 is 1
elif n == 0:
    print("Factorial of 0 is 1")

else:
    # iterate the for loop from 1 to n
    factorial = 1
    for i in range(1,n+1):
        # multiple the n with 1*2*3*...*n
        factorial = factorial*i
    # print the factorial of n
    print("Factorial of",n,"is",factorial)

Output

Factorial of 5 is 120

Using Recursion

Using recursion we find the factorial of a number by making a function named factorial that calls itself.

Program

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# python program to find the factorial of number using Recursion
# make a function named factorial
def factorial(n):
    if (n==1 or n==0):
        return 1 
    else: 
        # call the function again until the n ==1 or n ==0
        return(n * factorial(n - 1))  

n = 5
# call the function
print("Factorial of",n,"is",factorial(n))

Output

Factorial of 5 is 120

Using built-in function

factorial() is a in built function. To use factorial function we have to import math.

Program

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# python program to find the factorial of number using factorial() function
# import math
import math
n = 5
# use the math.factorial() function to find the factorial of any number
print("Factorial of",n,"is",math.factorial(n))

Output

Factorial of 5 is 120

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