Find the radius of convergence, $R,$ of the series.

${\displaystyle \underset{n=1}{\overset{}{}}}\frac{(-1{)}^n{7}^n}{\sqrt[\phantom{2}]{n}}{x}^n$

$R=$

Find the interval, I, of convergence of the series. $($Enter your answer using interval notation.$)$

$I=$