Python Program to Find the Factorial of a Number

Factorial of a number:

The product of all positive integers less than or equal to n is the factorial of a non-negative integer n, denoted by n! in mathematics:

n! = n * (n – 1) *(n – 2) * . . . . . . . . . . 3 * 2 * 1.

4 != 4 * 3 * 2 * 1

Examples:

Input:

number = 7

Output:

Factorial of 7 = 5040

Given a number , the task is to find the factorial of the given number

Finding Factorial of a Number

There are several ways to find factorial of a number in python some of them are:

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Method #1:Using for loop(Without Recursion)

Approach:

  • Create a variable say res and assign it to 1.
  • Using for loop and range,  Run a loop from 1 to n.
  • Multiply the res with the loop iterator value.

Below is the implementation:

# given number
num = 7
# initializing a variable res with 1
res = 1
# Traverse from 1 to n
for i in range(1, num+1):
    res = res*i
# print the factorial
print("Factorial of", num, "=", res)

Output:

Factorial of 7 = 5040

Method #2: Using recursion

To find the factorial of a given number, we will use recursion. We defined the factorial(num) function, which returns 1 if the entered value is 1 and 0 otherwise, until we get the factorial of a given number.

Below is the implementation:

# function which returns the factorial of given number
def facto(num):
    if(num == 1 or num == 0):
        return 1
    else:
        return num*facto(num-1)


# given number
num = 7
# passing the given num to facto function which returns the factorial of the number
res = facto(num)
# print the factorial
print("Factorial of", num, "=", res)

Output:

Factorial of 7 = 5040

Method #3 : Using Built in Python functions

Python has a built-in function

factorial (number)

which returns the factorial of given number.

Note: factorial function is available in math module

Below is the implementation:

# import math module
import math
# given number
num = 7
# finding factorial using Built in python function
res = math.factorial(num)
# print the factorial
print("Factorial of", num, "=", res)

Output:

Factorial of 7 = 5040

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