  We calculate the derived series of the Riordan group. To do that, we study a
nested sequence of its subgroups, herein denoted by $\mathcal G_k$. By means of
this sequence, we first obtain the n-th commutator subgroup of the Associated
subgroup. This fact allows us to get some related results about certain groups
of formal power series and to complete the proof of our main goal, Theorem 1 in
this paper.
