Let p≠3 be any prime. A classification of constacyclic codes of length 3ps over the finite field Fpm is provided. Based on this, the structures in terms of polynomial generators of all such constacyclic codes and their duals are established. Among other results, we show that self-dual cyclic codes of length 3ps exist only when p=2, and in such case, those self-dual codes are listed.
Dinh, Hai Q (2013). Structure of Repeated-Root Constacyclic Codes of Length 3p^s and Their Duals. Elsevier 313(9) 983-991. doi: 10.1016/J.DISC.2013.01.024. Retrieved from https://oaks.kent.edu/mathpubs/15