java

public class  {
    public static void main(String[] args) {
        float up = 2;
        float down = 1;//第一个分数的分母
        float fraction = up/down;
        float temp = 0;//用于包存分子分母之和
        float sum = 0;//结果
        for (int i=0; i < 20; i++) {//前二十项所以循环20-1次
            sum += fraction;//第一个
            temp = up + down;
            down = up;
            up = temp;
            fraction = up/down;
        }

        System.out.println("该序列前二十项之和为"+sum);
    }
}