1!+1/2!+1/3!+1/4!+....的前20项和

public class factorial2{    public static void main(String arg[]){    double a,b=1,c=0;    System.out.println("1!+1/2!+1/3!+1/4!+....的前20项和：");        for(a=1;a<=20;a++){            b*=1/a;            c+=b;        }        System.out.println(c);    }}