10001 students at an university
Source: IMO ShortList 2004, combinatorics problem 1
June 15, 2005
combinatoricsIMO Shortlistdouble counting
Problem Statement
There are students at an university. Some students join together to form several clubs (a student may belong to different clubs). Some clubs join together to form several societies (a club may belong to different societies). There are a total of societies. Suppose that the following conditions hold:i.) Each pair of students are in exactly one club.ii.) For each student and each society, the student is in exactly one club of the society.iii.) Each club has an odd number of students. In addition, a club with students ( is a positive integer) is
in exactly societies.Find all possible values of .Proposed by Guihua Gong, Puerto Rico