# Factorial calculation

suggest changeThe factorial of a number (denoted with !, as for instance 9!) is the multiplication of that number with the factorial of one lower. So, for instance, 9! = 9 x 8! = 9 x 8 x 7! = 9 x 8 x 7 x 6 x 5 x 4 x 3 x 2 x 1.

So in code that becomes, using recursion:

```
long Factorial(long x)
{
if (x < 1)
{
throw new OutOfRangeException("Factorial can only be used with positive numbers.");
}
if (x == 1)
{
return 1;
} else {
return x * Factorial(x - 1);
}
}
```

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Let me know.

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