java程序题：求1+2!+3!+...+20!的和

求1+2!+3!+...+20!的和  
public class lianxi21 {
public static void main(String[] args) {
    long sum = 0;
    long fac = 1;
    for(int i=1; i<=20; i++) {
     fac = fac * i;
     sum += fac;
    }
    System.out.println(sum);
}
}
 

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