In the previous article, we have discussed Python Program for Product of Maximum in First array and Minimum in Second

**Factorial:**

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=24

**Double Factorial:**

The product of all the integers from 1 to n with the same parity (odd or even) as n is the double factorial of a non-negative integer n. It is also known as a number’s semi factorial and is denoted by!!.

For example, **the double factorial of 7 is 7*5*3*1 = 105**

It is worth noting that as a result of this definition, 0!! = 1.

The double factorial for even number ‘n’ is:

The double factorial for odd number ‘n’ is:

Given a number ‘n’ and the task is to find the double factorial of a given number.

**Examples:**

**Example 1:**

**Input:**

Given number = 5

**Output:**

The double factorial of a given number{ 5 } = 15

**Example 2:**

**Input:**

Given number = 10

**Output:**

The double factorial of a given number{ 10 } = 3840

## Program for Double Factorial in Python

Below are the ways to find the double factorial of a given number.

### Method #1: Using For Loop (Static Input)

**Approach:**

- Give the number as static input and store it in a variable.
- Take a variable, initialize it with the value ‘1’, and store it in another variable say ‘c’.
- Loop from the given number to 0 in decreasing order with the stepsize of -2 using the for loop.
- Inside the loop multiply the above initialized variable c with the iterator value and store it in the same variable ‘c’.
- Print the double factorial of a given number.
- The Exit of the Program.

**Below is the implementation:**

# Give the number as static input and store it in a variable. numbr = 8 # Take a variable, initialize it with the value '1', and store it in another # variable say 'c'. c = 1 # Loop from the given number to 0 in decreasing order with the stepsize of -2 # using the for loop. for i in range(numbr, 0, -2): # Inside the loop multiply the above initialized variable c with the iterator value # and store it in the same variable 'c'. c *= i # Print the double factorial of a given number. print("The double factorial of a given number{", numbr, "} = ", c)

**Output:**

The double factorial of a given number{ 8 } = 384

### Method #2: Using For loop (User Input)

**Approach:**

- Give the number as user input using the int(input()) function and store it in a variable.
- Take a variable, initialize it with the value ‘1’, and store it in another variable say ‘c’.
- Loop from the given number to 0 in decreasing order with the stepsize of -2 using the for loop.
- Inside the loop multiply the above initialized variable c with the iterator value and store it in the same variable ‘c’.
- Print the double factorial of a given number.
- The Exit of the Program.

**Below is the implementation:**

# Give the number as user input using the int(input()) function and store it in a variable. numbr = int(input("Enter a random number = ")) # Take a variable, initialize it with the value '1', and store it in another # variable say 'c'. c = 1 # Loop from the given number to 0 in decreasing order with the stepsize of -2 # using the for loop. for i in range(numbr, 0, -2): # Inside the loop multiply the above initialized variable c with the iterator value # and store it in the same variable 'c'. c *= i # Print the double factorial of a given number. print("The double factorial of a given number{", numbr, "} = ", c)

**Output:**

Enter a random number = 7 The double factorial of a given number{ 7 } = 105

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