$729^{-\frac{2}{3}}$

$${\mathtt{729}}{\mathtt{\,-\,}}{\frac{{\mathtt{2}}}{{\mathtt{3}}}} = {\mathtt{728.333\: \!333\: \!333\: \!333\: \!333\: \!3}}$$

$${{\mathtt{729}}}^{{\mathtt{\,-\,}}\left({\frac{{\mathtt{2}}}{{\mathtt{3}}}}\right)} = {\mathtt{0.012\: \!345\: \!679\: \!012\: \!345\: \!7}}$$

If you want to enter the LaTex straight into the forum you do not need the dollar signs as the forum is already in math mode.

Click on the LaTex Formula button on the input ribbon and then insert your expression:

$$$729^{-\frac{2}{3}}$$ $