A mealy machine with polynomial growth of irrational degree

We consider a very simple Mealy machine ( two nontrivial states over a two-symbol alphabet), and derive some properties of the semigroup it generates. It is an infinite, finitely generated semigroup, and we show that the growth function of its balls behaves asymptotically like l(alpha), for alpha = 1 + log 2/log 1+root 5/2 ; that the semigroup satisfies the identity g(6) = g(4); and that its lattice of two-sided ideals is a chain.