2/1，3/2，5/3，8/5，13/8，21/13...求出这个数列的前 20 项之和

package cskaoyan;
 
public class cskaoyan20 {
    @org.junit.Test
    public void sum() {
        double numerator = 2;
        double denominator = 1;
        double total = 0;
 
        for (int i = 0; i < 20; i++) {
            total += numerator / denominator;
            double temp = numerator;
            numerator = numerator + denominator;
            denominator = temp;
        }
 
        System.out.println("这个数列的前 20 项之和是" + total);
    }
}