package com.xiaowu.demo;

//求1+2!+3!+...+20!的和。
public class Demo21 {
    public static void main(String[] args) {
        sum(20);
    }

    public static void sum(int n) {
        long sum = 0;
        long fac = 1;
        for (int i = 1; i <= n; i++) {
            fac *= i;
            sum += fac;
        }
        System.out.println("1!到" + n + "!相加的和是： " + sum);
    }
}