The degrees of a system of parameters of the ring of invariants of a   binary form
  We consider the degrees of the elements of a homogeneous system of parameters for the ring of invariants of a binary form, give a divisibility condition, and a complete classification for forms of degree at most 8. 
Andries E. Brouwer and Jan Draisma and Mihaela Popoviciu
math.AC math.AG