3

Part of 2015 South East Mathematical Olympiad

Problems(1)

Arrange in a circle

Source: China Southeast Math Olympiad 2015 Day 1 P3

2015

positive integers

1,2, \ldots , 2015

to be a certain permutation which can be ordered in the circle such that the sum of any two adjacent numbers is a multiple of

4

or a multiple of

7

combinatoricsgraph theory