Repeated-root constacyclic codes of length 2ℓmpn2ℓmpn

For any different odd primes ℓ and p  , structure of constacyclic codes of length 2ℓmpn2ℓmpn over the finite field FqFq of characteristic p   and their duals is established in terms of their generator polynomials. Among other results, the characterization and enumeration of all linear complementary dual and self-dual constacyclic codes of length 2ℓmpn2ℓmpn are obtained.