Number of order ideals of type e^(1)_n.

Terms

a(0) =2a(1) =3a(2) =7a(3) =12a(4) =31a(5) =55a(6) =152a(7) =273a(8) =790a(9) =1428a(10) =4271a(11) =7752a(12) =23767a(13) =43263a(14) =135221a(15) =46675a(16) =782968a(17) =1430715a(18) =4598804a(19) =8414640a(20) =27332956a(21) =50067108a(22) =164081764