Due Monday November 4 in class.

Section 2.3: #9(e) (do r=4 and r=12 only)
Section 2.4: #9, #13 (hint: apply the pigeonhole principle to the remainders modulo n of 0, a₁, a₁ + a₂, …, a₁ + a₂ + … + a_n.)
Section 2.5: #3, #6, #9

Extra credit:

A. Show that for every n, there is a graph of order n which has exactly two vertices with the same degree, and all other degrees different.  Can you prove for which n and which k does there exist such a graph where the vertices with the same degree have degree k?