This is an example Prof. Boutin
$ e^{\frac{1}{2} j \pi n} \,\ $ is periodical because $ \omega = \frac{1}{2} \pi $ so $ \frac {\omega}{2 \pi} = \frac {1}{4} $
$ e^{\sqrt 2 j \pi n} $ is not periodical because $ \omega = \sqrt 2 \pi $ so $ \frac {\omega}{2 \pi} = \frac {1}{\sqrt 2} $
