i have to find a function $f(n)$ such that
$$1/\phi(n)= \sum\_{d\mid n} \frac{1}{d} f(\frac{n}{d}). $$

However, we know that :
 $$ \phi(n)= \mu\* \operatorname{Id}(n) $$
$$ \phi(n)= \sum\_{d\mid n}\frac{n}{d}\mu(d) $$
I have a feeling i need to use these equations but not sure how.