I am considering the discrete-time discrete-valued random process $X_n$ that consists of the sequences
Sequence1: 0 0 1 0 0 1 0 0 1 0 0 1 0 0 ... Sequence2: 1 0 0 1 0 0 1 0 0 1 0 0 1 0 ... Sequence3: 0 1 0 0 1 0 0 1 0 0 1 0 0 1 ...
with each sequence being chosen with equal probability $\frac{1}{3}$.
After determining that this process is not an i.i.d. random process, I am having trouble finding the joint PMF of $X_{n_1}$ and $X_{n_2}$. Any help would be greatly appreciated. Thanks!