Let R2=Fpm+uFpm, where u2=0. In this paper, we determine the algebraic structures of all skew constacyclic codes of lengths psand 2psover R2for special automorphisms. We also characterize the structure of (Euclidean) dual of some special skew constacyclic codes of length 2psand calculate the number of codewords of them. As a special case, if we restrict our attention to the polynomial ring R2[x], we obtain most of results for constacyclic codes of lengths psand 2psover R2
