If a₁, a₂,…,a_n , a_n+1,… are in GP and a_i > 0 ∀i , then \(\begin{vmatrix} a_n & a_{n+1} & a_{n+4}\\ a_{n+6} & a_{n+8} & a_{n+10}\\ a_{n+12} & a_{n+14} & a_{n+16}\\ \end{vmatrix}\) is equal to