Combinatorial mathematics is a branch of mathematics, which mainly studies the method of arranging or configuring discrete things according to certain rules. It solves four problems: ① whether an arrangement that meets certain conditions exists; (2) Determine the number of all possible permutations on the premise that the known solution exists; (3) give all possible arrangements; ④ When different arrangements have standards, find the best arrangement. These problems are also called existence, counting, arrangement and optimization problems. Combinatorial mathematics originated from mathematical entertainment and games. In China's myths and legends, Luo Shu Tu is equivalent to a Rubik's cube of order 3, and the sum of each row, column and diagonal elements is 15. This kind of figure is also called magic square. 10 In the late 3rd century, Yang Hui gave a magic square of order 3 ~ 10, which is called the vertical and horizontal plane. The problem of 36 officers put forward by L. Euler in18th century is an interesting mathematical problem. /kloc-in the mid-9th century, the problem of Kirkman 15 girls' walking was upgraded to a general Kirkman series, which has not been completely solved so far. Combinatorial mathematics has a long history, but it has developed slowly for a long time. In recent decades, with the development of computer science, planning theory, experimental design and other disciplines, it has stimulated the development of combinatorial mathematics and made it more vital. The basic formula of counting is as follows: (1) Take the permutation number of k from n different elements; Take the combination number of k in n different elements; N different elements are divided into R groups, so that the number of grouping methods that group I contains ki elements is fixed at.