Answer:
4
Step-by-step explanation:
pattern alternates between positive and negative values
also, each successive number is the square of the quotient of the value and the next value by 2
example, the square root of 1024 is 32
now take half of 32 to get 16, and then square it to get 256
the square root of 256 is 16
now take half of 16 to get 8, and then square it to get 64
