This is the number of longest common subsequences between two binary strings of the form 00...011...1.
This is a lower bound for A094837, equivalent to choosing first string (x "a"s followed by (n-x) "b"s) and second string (y "a"s followed by (n-y) "b"s).
a(3) is maximal with x=1, y=2, giving a(3) = C(2,1) * C(3-1,3-2). This is equivalent to the number of instances of length-2 common subsequences between "aab" and "abb".
