Homework 2

This assignment is due by the beginning of class on Wednesday, September 10^th. Be sure to review the homework guidelines before getting started.

• Prove that if $a^n-1$ is prime and $n>1$, then $a=2$.
• For an integer n, let $\nu(n)$ be the number of positive divisors of n. For example, the positive divisors of 6 are 1, 2, 3, 6, and so $\nu(6) = 4$. If n factors as $n = p_1^{a_1}\cdots p_r^{a_r}$, determine $\nu(n)$ — with explanation. Is it true that $\nu(nm) = \nu(n)\nu(m)$ for any pair of integers n and m?
• From Strayer, do the following problems:
  • 19
  • 30
  • 43
  • 44
  • 54 (c,d)
  • 55

It would also be good to get some practice on other problems, even though I won't be collecting them. For this, I'd suggest you take a look at the following problems

• Prove that if $a^n-1$ is prime, then n is prime. Together with the first problem in this assignment, this means that $a^n-1$ only has a chance of being prime if $a=2$ and n is prime.
• From Strayer, you might try
  • 24
  • 26
  • 36
  • 38
  • 47

Any other problems you want to work on are also good practice, so if these problems all seem to easy, try out some others on your own.