  Extending the analogous result of Cannon and Wagreich for the fundamental
groups of surfaces, we show that, for the l-regular graphs X associated to
regular tessellations of hyperbolic plane by m-gons, the denominators of the
growth series (which are rational and were computed by Floyd and Plotnick) are
reciprocal Salem polynomials. As a consequence, the growth rates of these
graphs are Salem numbers. We then derive some regularity properties for the
coefficients $a_n$ of the growth series: they satisfy
$$K\lambda^n-R<a_n<K\lambda^n+R$$ for some constants $K,R>0$, $\lambda>1$.

Group Theory