Repeated-Root Constacyclic Codes Of Length 3l^mp^s

Let p be a prime different from 3, and l be an odd prime different from 3 and p. In terms of generator polynomials, structures of constacyclic codes and their duals of length 3l^mp^s over  are established, where q is a power of p. We discuss the enumeration of all cyclic codes of length 3 · 2^sl^m, that generalizes the construction of (2016), which is the special case of m = 1. In addition, as an application, the characterization and enumeration of all linear complementary dual cyclic codes of length 6l^mp^s over  are obtained.