Bounds on Multipartite Concurrence and Tangle
  We present an analytical lower bound of multipartite concurrence based on the generalized Bloch representations of density matrices. It is shown that the lower bound can be used as an effective entanglement witness of genuine multipartite entanglement. Tight lower and upper bounds for multipartite tangles are also derived. Since the lower bounds depend on just part of the correlation tensors, the result is experimentally feasible. 
Jing Wang, Ming Li, Hongfang Li, Shao-Ming Fei, and Xianqing Li-Jost
quant-ph