# Python Program to Find Factorial of Number Using Recursion

Factorial recursion is a method in which a function directly or indirectly calls itself. In mathematics, Factorial means the product of all the positive integers from 1 to that number. An exclamation mark is used after the integer to show that it’s a factorial.

For example, factorial eight is 8! So, it means multiplication of all the integers from 8 to 1 that equals 40320. Factorial of zero is 1. We can find a factorial of a number using python. There are various ways of finding; The Factorial of a number in python. Among which recursion is the most commonly used.

Source: Self

## Factorial Function in Python

### Source Code: Python Program to find factorial of a number using recursive function

                    
def recursive_factorial(n):
if n == 1:
return n
else:
return n*recursive_factorial(n-1)     #function calling itself

#taking input from the user
number = int(input("User Input : "))
print("The factorial of", number, "is", recursive_factorial(number))




### Output :

                    
User Input: 4
The factorial of 4 is 24



### Source code: Displaying an error message if a user inputs a negative integer

                    
def recursive_factorial(n):
if n == 1:
return n
else:
return n*recursive_factorial(n-1)

#taking input from the user
number = int(input("User input : "))

# If the user input negative integer
if number < 0:
else:
print("The factorial of", number, "is", recursive_factorial(number))




### Output:

                    
User input : -1




### Source code: Factorial of zero is 1.

                    
def recursive_factorial(n):
if n == 1:
return n
else:
return n*recursive_factorial(n-1)

#taking input from the user
number = int(input("User Input : ")

# If the user input negative integer
if number < 0:

# If the user inputs 0
elif number == 0:
print("The factorial of 0 is 1")
else:
print("The factorial of", number, "is", recursive_factorial(number))




### Output:

                    
User Input : 0
The factorial of 0 is 1



## FAQs on Factorial Recursion

### What is Factorial recursion?

Factorial of a positive integer is the multiplication of all integers from that number to 1.

Factorial is represented by an exclamation mark.

If the user inputs a number let’s assume the number is n, so n factorial is n! = n * (n-1)!

For example:

factorial of 3 is

3! = 3 * 2 * 1. which equals 6.

There is no factorial output for negative integers

So, the factorial of 0 is 1

### How does Factorial recursion work?

Factorial of a number is the multiplication of all the integers from that number to 1.

Source: Self

The input value (positive integer) is passed; as a parameter to the factorial function.

So, Whenever the function runs, It multiplies the value of a parameter and recursively calls the function itself while decrementing the parameter value by 1.

Once the value becomes 0 the function returns 1 (as the factorial of 0 is 1) and returns the multiplier value that is the factorial of an inputted number.

How do you find the Recursive Factorial?

Factorial recursion is a function that is defined in such a way that it calls itself. Until it returns the factorial of the number passed as a parameter to the function.

Formula to calculate Factorial recursion.

n!=n * (n-1)!  also [n!=1 if n=0]

factorial of 0 is 1

There is no factorial output for negative integers.

### What is recursion? Write a program for factorial calculation.

Recursion is a concept where you can loop through data to get a result. A problematic function can be broken down, into smaller sub-parts by using recursion.

##### Program for factorial calculation:

                    
def recursive_factorial(n):

if n == 1:

return n

else:

return n*recursive_factorial(n-1)

num = int(input("User Input :"))

print("The factorial of", num, "is", recursive_factorial(num))

Output
User Input :5

The factorial of 5 is 120


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