Twisted Angles for Central Configurations Formed By Two Twisted Regular   Polygons
  In this paper, we study the necessary conditions and sufficient conditions for the twisted angles of the central configurations formed by two twisted regular polygons, specially, we prove that for the 2N-body problems, the twisted angles must be$\theta=0 {or} \theta=\pi/N$. 
Yu Xiang and Zhang Shiqing
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