Homework Statement
Is U(13) cyclic? Is U(15) cyclic?
2. The attempt at a solution
The units in U(13): {1,2,3,4,5,6,7,8,9,10,11,12} U(13) is not cyclic because it is prime?
U15:{1,2,4,7,8,11,13,14} and there are no generators either? I do not think I am correct with this though.