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

Terms

a(0) =1a(1) =4a(2) =10a(3) =21a(4) =40a(5) =73a(6) =130a(7) =228a(8) =396a(9) =684a(10) =1178a(11) =2025a(12) =3476a(13) =5961a(14) =10218a(15) =17512a(16) =30010a(17) =51424a(18) =88114a(19) =150977a(20) =258684a(21) =443225a(22) =759410a(23) =1301148a(24) =2229340a(25) =3819668a(26) =6544474a(27) =11213049a(28) =19212000a(29) =32917085