(possibly the earliest publication to use double factorial notation) states that the double factorial was originally introduced in order to simplify the expression of certain trigonometric integrals arise in the derivation of the Wallis merchandise. The term odd factorial is sometimes used for the double factorial of an odd number.

COMING SOON!

```
// C++ program to find factorial of given number
#include<iostream>
// function to find factorial of given number
unsigned int factorial(unsigned int n) {
if (n == 0)
return 1;
return n * factorial(n - 1);
}
// Driver code
int main() {
int num = 5;
std::cout << "Factorial of " << num << " is " << factorial(num)
<< std::endl;
return 0;
}
```