On Mon, May 7, 2012 at 12:35 PM, Mark Dickinson <dickinsm at gmail.com> wrote: > will almost always be one less than a power of 2 and powers of 2 are > always congruent to 1, 2 or 4 modulo 5, we're safe. Bah. That should have read "1, 2, 3 or 4 modulo 5".