Abstract. We discuss the properties and the permutation behaviour of the reversed Dickson polynomials of the (k + 1)-th kind D n,k (1, x) over finite fields. The results in this paper unify and generalize several recently discovered results on reversed Dickson polynomials over finite fields.
IntroductionLet p be a prime and q a power of p. Let F q be the finite field with q elements. A polynomial f ∈ F q [x] is called a permutation polynomial (PP) of F q if the associated mapping x → f (x) from F q to F q is a permutation of F q . Permutation polynomials over finite fields have important applications in Coding Theory, Cryptography, Finite Geometry, Combinatorics and Computer Science, among other fields.Recently, reversed Dickson polynomials over finite fields have been studied extensively by many for their general properties and permutation behaviour. The concept of the reversed Dickson polynomial D n (a, x) was first introduced by Hou, Mullen, Sellers and Yucas in [5] by reversing the roles of the variable and the parameter in the Dickson polynomial D n (x, a).The n-th reversed Dickson polynomial of the first kind D n (a, x) is defined bywhere a ∈ F q is a parameter. In [5], it was shown that the reversed Dickson polynomials of the first kind are closely related to Almost Perfect Nonlinear (APN) functions which have applications in cryptography. Hou and Ly found more properties of the reversed Dickson polynomials of the first kind and necessary conditions for them to be a permutation of F q ; see [4].By reversing the roles of the variable and the parameter in the Dickson polynomial of the second kind E n (x, a), the n-th reversed Dickson polynomial of the second kind E n (a, x) can be defined byn − i i (−x) i a n−2i , 2010 Mathematics Subject Classification. 11T06, 11T55.