1/4 -1/3 7/16 -13/25 7/12 1/4 -3/9 7/16 -13/25 21/36(1²-0)/2² -(2²-1)/3² (3²-2)/4² -(4²-3)/5² (5²-4)/6²可以看出第8个数是 -(8²-7)/9² = -19/27