Subsequence of $\sin n$

Subsequence of $\sin n$

Find one subsequence of $a_n= \sin n$ and prove it.
I know that for all $n_1<n_2<n_3<\dots$, then $a_{n_1},a_{n_2},...$ is the
sub-sequence of $a_n$. But I don't know how to use this definition in this
problem