Let's find the inflection points, we'll need to solve the equation for this
$$\frac{d^{2}}{d n^{2}} f{\left(n \right)} = 0$$
(the second derivative equals zero),
the roots of this equation will be the inflection points for the specified function graph:
$$\frac{d^{2}}{d n^{2}} f{\left(n \right)} = $$
the second derivative$$\frac{- \left(-1\right)^{n} \pi^{2} - \frac{2 \left(-1\right)^{n} i \pi}{n} + \frac{2 \left(\left(-1\right)^{n} + 1\right)}{n^{2}}}{n} = 0$$
Solve this equationSolutions are not found,
maybe, the function has no inflections