By constructing a Gray map, a class of constacyclic codes over ring R = R + vR is studied. Using cyclic codes and negacyclic codes of length p s over ring R , the structure of (1−2 v )-constacyclic codes and dual codes of length p s over ring R are given, the Gray images of (1 − 2 v )-constacyclic codes in a particular case are also studied. It is shown that linear codes of length p s over ring R are (1−2 v )-constacyclic codes if and only if their Gray images are distance-invariant cyclic codes of length 2 p s over ring R .
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