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On the crossing numbers of join of the special graph on six vertices with nK_1, P_n or C_n

ZHOU Zhidong1,*   LI Long1   

  1. 2. College of Mathematics and Statistics, Hengyang Normal University, Hengyang 421002, Hunan, China
  • Received:2016-02-29 Online:2016-12-15 Published:2016-12-15

Abstract:

The crossing numbers of a graph is a vital parameter and a hard problem in the forefront of topological graph theory.  Determining the crossing number of an arbitrary graphs is NP-complete problem. Because of its difficultly, the classes of graphs whose crossing number have been determined are very scarce. In this paper, for the special graph Q on six vertices, we through the disk drawing method to prove that the crossing numbers of its join with n isolated vertices as well as with the path P_{n} and with the cycle C_{n} are cr(Q+nK_{1})=Z(6,n)+2\lfloor\frac{n}{2}\rfloor, cr(Q+P_{n})=Z(6,n)+2\lfloor\frac{n}{2}\rfloor+1 and cr(Q+C_{n})=Z(6,n)+2\lfloor\frac{n}{2}\rfloor+3, respectively.

Key words: drawing, crossing number, disk drawing, joint graph, path, cycle