1、The factorial of a non-negative integer n, denoted by n!, is the product of all positive integers less than or equal to n.
非负整数n的阶乘，记作n！，是小于或等于n的所有正整数的乘积。
2、The factorial function is commonly used in math and combinatorics to solve problems involving permutations and combinations.
阶乘函数常用于数学和组合数学中，用于求解涉及排列和组合的问题。