Growth functions of groups have been studied intensively in geometric group theory.  Regarded up to affine rescaling, they give a group invariant called the growth rate, and there are long-standing questions about possible growth rates for finitely generated groups.  Another stream of questions asks whether the growth values satisfy a recursion, a property which is called rational growth and depends on the choice of generators.  I will survey the area and discuss the classic proofs that hyperbolic groups and virtually abelian groups have rational growth in any generators

Growth functions of groups have been studied intensively in geometric group theory.  Regarded up to affine rescaling, they give a group invariant called the growth rate, and there are long-standing questions about possible growth rates for finitely generated groups.  Another stream of questions asks whether the growth values satisfy a recursion, a property which is called rational growth and depends on the choice of generators.  I will survey the area and discuss the classic proofs that hyperbolic groups and virtually abelian groups have rational growth in any generators