Monogamous nature of symmetric N-qubit states of the W-class:   Concurrence and Negativity Tangle
  Using Majorana representation of symmetric N-qubit pure states, we have examined the monogamous nature of the family of states with two-distinct spinors, the W-class of states. We have evaluated the N-concurrence tangle and showed that all the states in this family have vanishing concurrence tangle. The negativity tangle for the W-class of states is shown to be non-zero illustrating the fact that concurrence tangle underestimates the residual entanglement in a pure N-qubit state. 
P.J. Geetha, K.O. Yashodamma and Sudha
quant-ph