For any non-zero natural integer $n$, we set
$$\omega(n) = \operatorname{Card}\{p \text{ prime} : p \mid n\} = \sum_{\substack{p \mid n \\ p \text{ prime}}} 1.$$
Show that
$$\frac{1}{x} \sum_{n \leqslant x} \left(\omega(n) - \ln_{2}(x)\right)^{2} \underset{x \rightarrow +\infty}{=} \frac{1}{x}\left(\sum_{n \leqslant x} \omega(n)^{2}\right) - \ln_{2}(x)^{2} + O\left(\ln_{2}(x)\right).$$