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

We exhibit a two-parameter class of states ρ(α,γ) in a 2 ⊗ n quantum system for n ≥ 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 2 ⊗ n quantum system. We calculate the negativity of ρ(α,γ), 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 ρ(α,γ) cannot exceed its negativity.