You can create elements of this group by coercing regular integers into U, such as with the statement a = U(7). Determine the elements of the cyclic subgroup of U generated by 7 with a list comprehension as follows:
\begin{verbatim}
R = Integers(40)
a = R(7)
[a^i for i in srange(16)]
\end{verbatim}
What is the order of 7 in U(40)?