1,-1,-2,3,-5,-8,13,（）,（）

fibonacci sequence
Don't look at the positive and negative
Look at the absolute value
It's 1 1 2 3 5 8 13
The sum of the first two numbers equals the last one
So the absolute values are 21 and 34
The sign is + -- + --
So 1, - 1, - 2,3, - 5, - 8,13, (- 21), (- 34)