If ${\tan }^2<!--\; \; -->\mathrm{\theta <!--\; \theta \; -->}-<!--\; -\; -->5\sec <!--\; \; -->\mathrm{\theta <!--\; \theta \; -->}=1$ has exactly 7 solutions in the interval $[0,\frac{n\mathrm{\pi <!--\; \pi \; -->}}{2}]$, for the least value of $n\in <!--\; \in \; -->N$, then $\underset{\mathrm{k}=1}{\overset{\mathrm{n}}{\sum <!--\; \sum \; -->}}\frac{\mathrm{k}}{2^{\mathrm{n}}}$ is equal to