Let $S$ = { $x_1$ , $x_2$ } be the solutions of the equation $x^2-2*a*x -1 = 0 $ , where $a$ is a positive integer.Prove that for any $ n \in\mathbb{N} $ the expression $ E=\frac{1}{8}$($x_1^{2n}-x_2^{2n}$)($x_1^{4n}-x_2^{4n}$) is a product of consecutive numbers.