Dual and self-dual negacyclic codes of even length over

In this paper, we determine the structure of negacyclic codes of even length over the ring Z 2 a and their dual codes. Furthermore we study self-dual negacyclic codes of even length over Z 2 a . A necessary and sufficient condition for the existence of nontrivial self-dual negacyclic codes is given, and the number of the self-dual negacyclic codes for a given even length is determined.