In mathematics, the factorial of a positive integer N, denoted by N !, is the merchandise of all positive integers less than or equal to N. The factorial operation is encountered in many areas of mathematics, notably in combinatorics, algebra, and mathematical analysis. In 1677, Fabian Stedman described factorials as apply to change ringing, a musical art involve the ringing of many tuned Bell. Factorials were used to count permutations at least as early as the 12th century, by Indian scholars. insomuch that a compleat Peal of changes on one number seemeth to be formed by unite of the compleat Peals on all lesser numbers into one entire body.

COMING SOON!

```
using System;
namespace Algorithms.Numeric
{
/// <summary>
/// The factorial of a positive integer n, denoted by n!,
/// is the product of all positive integers less than or equal to n.
/// </summary>
public static class Factorial
{
/// <summary>
/// Calculates factorial of a number.
/// </summary>
/// <param name="num">Input number.</param>
/// <returns>Factorial of input number.</returns>
public static long Calculate(int num)
{
if (num < 0)
{
throw new ArgumentException("Only for num >= 0");
}
return num == 0 ? 1 : num * Calculate(num - 1);
}
}
}
```