Find the domain of:

$\displaystyle {f{{\left({x}\right)}}}={\tan{{\left(\frac{{1}}{{9}}{x}-\frac{{1}}{{7}}\right)}}}$

 $\displaystyle {D}_{{f}}={\left\lbrace{x}{\mid}{x}\ne\right.}$ $\displaystyle ,{n}\in\mathbb{Z}{\rbrace}$ 

Your solution should be an expression in terms of $\displaystyle {n}$ such that $\displaystyle {n}$ is an integer.