Poincaré series for hyperbolic reflection group with Coxeter diagram shown in Comments.

Terms

a(0) =1a(1) =4a(2) =9a(3) =17a(4) =29a(5) =47a(6) =74a(7) =113a(8) =170a(9) =253a(10) =374a(11) =550a(12) =804a(13) =1171a(14) =1702a(15) =2472a(16) =3588a(17) =5204a(18) =7545a(19) =10936a(20) =15848a(21) =22962a(22) =33265a(23) =48188a(24) =69803a(25) =101112a(26) =146461a(27) =212145a(28) =307283a(29) =445083