The Noether number for the groups with a cyclic subgroup of index two
  The exact degree bound for the generators of rings of polynomial invariants is determined for the finite, non-cyclic groups having a cyclic subgroup of index two. It is proved that the Noether number of these groups equals one half the order of the group plus 1 or 2. 
K. Cziszter and M. Domokos
math.RT math.AC