geometric series

There are 11 terms and the common ratio is -2. Using the geometric series calculator, the answer is 683.

:D

Using algebra, we can see after subtracting a few numbers, we notice there are 10 numbers, therefore there are 5 pairs and one number.

$ -1, -4, -16, -64, -256, and 1024$

 

$1-2, 4-8, 16-32, 64-128, 256-512, 1024

 

using normal subtraction 

We get 

$683$