Entanglement for a two-parameter class of states in 2 ⊗ n quantum system

We exhibit a two-parameter class of states rho(alpha,gamma) in a 2 circle times n quantum system for n greater than or equal to 3, which can be obtained from an arbitrary state by means of local quantum operations and classical communication, and which are invariant under all bilateral operations on a 10 n quantum system. We calculate the negativity of p(alpha,gamma), and a lower bound and a tight upper bound on its entanglement of formation. It follows from this calculation that the entanglement of formation of rho(alpha,gamma) cannot exceed its negativity.