On Type IV self-dual codes over Z4

Recently, Type IV self-dual codes over rings of order 4 have been introduced as self-dual codes over the rings with the property that all Hamming weights are even. All Type IV self-dual codes over Z4 of lengths up to 16 are known. In this paper, the classification of such codes of length 20 is given. The highest minimum Hamming, Lee and Euclidean weights of Type IV Z4-codes of lengths up to 40 and length 56 are also determined.