@沙尘暴
∑i=1nfi=fn−2−1\sum_{i=1}^n f_i = f_{n-2}-1∑i=1nfi=fn−2−1
您上面这个式子有问题吧，应该是：
∑i=1nfi=fn+2−1\sum_{i=1}^n f_i = f_{n+2}-1∑i=1nfi=fn+2−1
