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.
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:
print("Bad Input")
else:
print("The factorial of", number, "is", recursive_factorial(number))
Output:
User input : -1
Bad Input
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:
print("Bad Input")
# 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.
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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