What does the ! mean in math formulas?

by Richard
(USA)

Question

I was taking an online test and the question was what does 4! mean. Do you know what this means?

Answer

It's the factorial sign (!). 4! simply means that we are taking the product of 4×3×2×1. See some examples below:

1! = 1
2! = 2×1 = 2
3! = 3×2×1 = 6
4! = 4×3×2×1 = 24
5! = 5×4×3×2×1 = 120

In general:

n! = n×(n-1)× (n-2)× .... ×3×2×1

That's all.