Find sequence 1 / 2,1 / 4, - 5 / 8,13 / 16, - 29 / 32,61 / 64 General term of

Find sequence 1 / 2,1 / 4, - 5 / 8,13 / 16, - 29 / 32,61 / 64 General term of

(-1)^n * (2^n - 3)/( 2^n)