$\frac{\left(6x^{3}-1\right)^{9}}{19683x^{18}}$

$512x^{9}-768x^{6}+512x^{3}-\frac{1792}{9}+\frac{448}{9x^{3}}-\frac{224}{27x^{6}}+\frac{224}{243x^{9}}-\frac{16}{243x^{12}}+\frac{2}{729x^{15}}-\frac{1}{19683x^{18}}$