Suppose that given n numbers you want to arrange them in a circle such that each number is adjacent to every other number exactly once. You may use each number multiple times. For example, for 1,2,3,4,5 you can put them in the order 1,2,3,4,5,3,1,4,2,5.
(a) Can you produce a similar arrangement for 1, 2, 3, 4, 5, 6, 7?
(b) Use the theorem for Eulerian Circuits to show that there is a solution for n numbers if and only if n is odd.