hey dan,
challonge.com will format a bracket with any number of entrants and award byes randomly if that is the way you want to go. you can also do what I did when we were short on the hustle this time and award the byes yourself, and then put the rest of the group in the random generator and then recreate the bracket in challonge or somewhere else.
32 will probably be your easiest choice. hope that helps...