  Pairwise correlation is really an important property for multi-qubit states.
For the two-qubit X states extracted from Dicke states and their superposition
states, we obtain a compact expression of the quantum discord by numerical
check. We then apply the expression to discuss the quantum correlation of the
reduced two-qubit states of Dicke states and their superpositions, and the
results are compared with those obtained by entanglement of formation, which is
a quantum entanglement measure.
