Write the sum using sigma notation.

${\displaystyle \underset{k=1}{\overset{n}{}}}\frac{\frac{\sqrt[\phantom{2}]{1}}{1^2}\frac{\sqrt[\phantom{2}]{2}}{2^2}\frac{\sqrt[\phantom{2}]{3}}{3^2}\text{c}\text{d}\text{o}\text{t}\text{s}\frac{\sqrt[\phantom{2}]{n}}{n^2}}{x}$