Thanks for running these competitions, its great to be a winner of something for once! Here is my go at this weeks quiz

I think the answer is -2

The change from the previous number is +1 , - 2 , +3 , -4 , +5 , -6

In equation form Xn = X(n-1) + (-1)^n* (n-1)

So the seventh number X7 = 4 + -1 * 6 = -2