Lower central series of the Riordan group over the field with two elements

Abstract: The Riordan group ${\cal R}$ over the field ${\mathbb F}_2$ is a split extension of the Appell subgroup by the Nottingham group ${\cal N}({\mathbb F}_2)$. Using the lower central series of the Nottingham group obtained by C. Leedham-Green and S. McKay, the lower central series of ${\cal R}({\mathbb F}_2)$ is calculated. It is also proved that the abelianization of the Riordan group over any commutative ring with identity is isomorphic to the direct product of the abelianization of the corresponding Lagrange subgroup, the additive group of the ring, and its multiplicative groups of units.