Rating:

Use the matrix equation for fibonacci.

$$\begin{pmatrix}C_n \\\\ C_{n-1}\end{pmatrix} = \begin{pmatrix}6 & 1 \\\\ 1 & 0\end{pmatrix}^{n-1} \begin{pmatrix}1 \\\\ 0\end{pmatrix}$$

I don't remember