Let $A = \left[ \begin{array} { l l l } 1 & 0 & 0 \\ 0 & \alpha & \beta \\ 0 & \beta & \alpha \end{array} \right]$ and $| 2 A | ^ { 3 } = 2 ^ { 21 }$ where $\alpha , \beta \in Z$, Then a value of $\alpha$ is\\ (1) 3\\ (2) 5\\ (3) 17\\ (4) 9