7. Given the function $f(x)=\frac{25^{x}}{25^{x}+5}$. Then $\sum_{k=1}^{2016} f\left(\frac{k}{2017}\right)=$ $\qquad$ .
二、7.1008.
Notice that, when $0<x<1$, we always have
$$
f(x)+f(1-x)=1 \text {. }
$$

Therefore, the original expression $=1008$.