8. Given the set
$$
\begin{array}{c}
A_{k}=\left\{2^{k-1}+\sum_{i=0}^{k-2} a_{i} 2^{a_{i}+i} \mid a_{i} \in\{0,1\},\right. \\
i=0,1, \cdots, k-2\} .
\end{array}
$$

Let $n_{k}$ denote the sum of all elements in the set $A_{k}$. Then $\sum_{k=1}^{2015} n_{k}=$ $\qquad$