So what is factorial? Suppose we want to calculate the factorial of the number 9. To do this, multiply all the numbers from 1 to 9.
1⋅2⋅3⋅4⋅5⋅6⋅7⋅8⋅9=362 880
This is the factorial. Thus, to find the factorial of any number, you need to multiply all numbers from 1 to this number.