In , Kellerhals and Perren conjectured that the growth rates of cocompact hyperbolic Coxeter groups are Perron numbers. By results of Floyd, Parry, Kolpakov, Nonaka-Kellerhals, Komori and the author , , , , , , , , the growth rates of 2- and 3-dimensional hyperbolic Coxeter groups are always Perron numbers. Kolpakov and Talambutsa showed that the growth rates of right-angled Coxeter groups are Perron numbers . For certain families of 4-dimensional cocompact hyperbolic Coxeter groups, the conjecture holds as well (see ,  and also ). In this paper, we construct an infinite sequence of ideal non-simple hyperbolic Coxeter 4-polytopes giving rise to growth rates which are distinct Perron numbers. This is the first explicit example of an infinite family of non-compact finite volume Coxeter polytopes in hyperbolic 4-space whose growth rates are of the conjectured arithmetic nature as well.
"An infinite sequence of ideal hyperbolic Coxeter 4-polytopes and Perron numbers." Kodai Math. J. 42 (2) 332 - 357, June 2019. https://doi.org/10.2996/kmj/1562032833