Re: [math-fun] Characterizing polys which permute GF(p)

The original question plus (ax+b)/(cx+d)brings up the question: Which rational functions over GF(n) (n = prime power) are permutations of GF(n) ? —Dan ———— P.S. Is there any way to define an infinite power series over a finite field, or some kind of completion of it?

On Mar 20, 2016, at 12:36 PM, rcs@xmission.com wrote:

The patched-reciprocal R(x) = {1/x, except R(0)=0} is a permutation, so probably all the (ax+b)/(cx+d) are too, with a similar patch, and excluding p|ad-bc.