1 public class Factorial {
 2 
 3     public static void main(String[] args) {
 4         int n = 20;
 5         double sumFactorial = 0.0;
 6         while (n > 0) {
 7             sumFactorial += (1.0 / calculateFactorial(n));
 8             n--;
 9         }
10         System.out.println("1+1/2!+1/3!+...+1/20!=" + sumFactorial);
11 
12     }
13 
14     public static long calculateFactorial(int num) {// 计算数的阶乘，由于20的阶乘超过了int所表示数的范围，所以这里用long
15         long sum = 1L;
16         while (num > 0) {
17             sum *= num;
18             num--;
19         }
20         return sum;
21     }
22 
23 }