求1+2!+3!+...+20!的和

1.程序分析：此程序只是把累加变成了累乘。

public class Ex21 {
    static long sum = 0;
    static long fac = 0;
    public static void main(String[] args) {
        long sum = 0;
        long fac = 1;
        for(int i=1; i<=10; i++) {
            fac = fac * i;
            sum += fac;
        }
        System.out.println(sum);
    }
}