Number of commutative elements in Coxeter group H_n.

Terms

a(0) =1a(1) =2a(2) =9a(3) =44a(4) =195a(5) =804a(6) =3185a(7) =12368a(8) =47607a(9) =182720a(10) =701349a(11) =2695978a(12) =10384231a(13) =40083848a(14) =155052001a(15) =600949336a(16) =2333344095a(17) =9074611032a(18) =35344215245a(19) =137844431690a(20) =538253680159