Number of order ideals of type e^(0)_n.

Terms

a(0) =2a(1) =4a(2) =7a(3) =17a(4) =30a(5) =80a(6) =143a(7) =404a(8) =728a(9) =2140a(10) =3876a(11) =11729a(12) =21318a(13) =65952a(14) =120175a(15) =378321a(16) =690690a(17) =2205168a(18) =4032015a(19) =13023324a(20) =23841480a(21) =77761008a(22) =142498692