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.pri
package com.xiaowu.demo; //利用递归方法求5!. public class Demo22 { public static void main(String[] args) { int n = 5; long s = sum(n); System.out.println(n + "!= " + s); } public static long sum(int n) { long s = 1; if (n == 1||n==0) { s = 1; } else {