$\begin{array}{l}\phantom{-x^{2}+16;}{-x^{3}\phantom{-;x^n}-16x\phantom{;}\phantom{-;x^n}}\\-x^{2}+16\overline{\smash{)}\phantom{;}x^{5}\phantom{-;x^n}\phantom{-;x^n}\phantom{-;x^n}\phantom{-;x^n}\phantom{-;x^n}}\\\phantom{-x^{2}+16;}\underline{-x^{5}\phantom{-;x^n}+16x^{3}\phantom{-;x^n}\phantom{-;x^n}\phantom{-;x^n}}\\\phantom{-x^{5}+16x^{3};}\phantom{;}16x^{3}\phantom{-;x^n}\phantom{-;x^n}\phantom{-;x^n}\\\phantom{-x^{2}+16-;x^n;}\underline{-16x^{3}\phantom{-;x^n}+256x\phantom{;}\phantom{-;x^n}}\\\phantom{;-16x^{3}+256x\phantom{;}-;x^n;}\phantom{;}256x\phantom{;}\phantom{-;x^n}\\\end{array}$

$-x^{3}-16x+\frac{256x}{16-x^2}$