R program to Find the Factorial of a Number Using Recursion

The factorial of a number is the product of all the integers from 1 to the number.

For example, the factorial of 6 (denoted as 6!) as

1 * 2 * 3 * 4 * 5 * 6 = 720

Factorial is not defined for negative numbers and the factorial of zero is one, 0! = 1.

In this example, the factorial of a number is calculated using a recursive function. However, you can also calculate it without the recursive function.

Learn more about how to find the factorial of a number without recursion.

Example: Find Factorial of a number using recursion

recur_factorial <- function(n) {
    if(n <= 1) {
        return(1)
    } else { 
        return(n * recur_factorial(n-1))
    }
}

Output

> recur_factorial(5)
[1] 120

Here, we ask the user for a number and use recursive function recur_factorial() to compute the product upto that number.

Lets suppose the user passes 5 to the function.

Inside the recur_factorial(), the number 5 is multiplied to the factorial of (5 - 1 = 4).

4 is multiplied again to the factorial of (4 - 1 = 3). This goes on until the number reaches 1.

Now, all previous functions of 2, 3, 4 and 5 returns the result one by one giving you the final result 1 * 2 * 3 * 4 * 5, which equals 120.