13. 已知$f\left(x\right)=2sin\left(ax+\theta \right)$（$a\in Z$，$0\le \theta <2\pi$）是偶函数，$f\left(x\right)$在区间$\left(0,\frac{\pi }{2}\right)$单调递增．则$\theta =$__________，$f\left(\frac{2\pi }{3}\right)=$__________．