Improved average and almost-all bounds for $G(n)$

In this paper we study the least positive integer $G(n)$ such that the integers $a\leq G(n)$ with $(a,n)=1$ generate $(\mathbb Z/n\mathbb Z)^\times$. We prove that, for every $\varepsilon>0$, \[ \sum_{n\leq x}G(n)\ll_\varepsilon x(\log x)^{8/3+\varepsilon}, \] improving the previously known bound