$\begin{array}{1 1}\sqrt 7.(\sqrt 3^n-1)(\sqrt 3+1) \\ \frac{\sqrt 7}{2}.(\sqrt 3^n-1)(\sqrt 3-1) \\\frac{\sqrt 7}{2}.(3^n-1) \\ \frac{\sqrt 7}{2}.(\sqrt 3^n-1)(\sqrt 3+1) \end{array} $
