Bi-Element Subsequence

First note that, taking any non-empty subset of $\{ 1, 2, \cdots, n \}$gives us a subsequence, namely the subsequence indices from that set. So we first count the subsequences containing only one distinct value. Suppose the array has value $x$ at $k$ indices, then any non-empty subset of those $k$ indices will create a subsequence containing only $x$. Hence number of subsequence containing only one value is $\sum _x 2^{cnt_x} - 1$where $cnt_x$ is the count of occurrences of $x$.

For the subsequences containing exactly two distinct values, we take all possible pairwise product of $2^{cnt_x}-1$ and sum them. All of this needs to be done modulo $10^9+7$