On Sat, Aug 1, 2009 at 5:33 PM, David Wilson<davidwwilson at comcast.net> wrote: > Theorem: For prime p > > p does not divide choose(2n, n) <=> all p-ary digits of n are < p/2. That's a trivial consequence of Lucas' Theorem: http://en.wikipedia.org/wiki/Lucas_theorem Regards, Max