Lefschetz zeta function

Let $f$ be a function. The Lefschetz zeta function is $$\zeta_f(z)=\exp \left( \displaystyle\sum_{k=0}^{\infty} L(f^n)\dfrac{z^n}{n} \right),$$ where $L(f^n)$ is the Lefschetz number of the $n$th iterate of $f$