In mathematics, the exclamation point means factorial. Factorial multiplication refers to the cumulative multiplication from the number 1 to the required number n, and the result is the factorial of n. In 1808, Keyston Kaman introduced this notation.

The formula of factorial: n! =1× 2× 3× …× n. The factor can also be defined recursively: 0! = 1，n！ =(n- 1)！ ×n .

For example, to find the value of 1×2×3×4…×n, it can be expressed by factorial: n! = 1×2×3×…×(n- 1)n or n! =(n- 1)！ ×n .