The structure of V(?($ZA_n$)) is known when $nleq6$. If n = 5 or 6, then a complete set of generators of V (?($ZA_n$)) has been deter-mined. In this study, it was shown that V (?($ZA_n$)) is trivial when n = 7, 8 or 9 and it is generated by a single unit u when n = 10 or 11: This unit u is characterized explicitly for n = 10 or 11 by using irreducible characters of $A_n$.