Numbers of closed affine (a.k.a. BCK) lambda terms of natural size n.

Terms

a(0) =0a(1) =0a(2) =1a(3) =1a(4) =2a(5) =5a(6) =12a(7) =25a(8) =64a(9) =166a(10) =405a(11) =1050a(12) =2763a(13) =7239a(14) =19190a(15) =51457a(16) =138538a(17) =374972a(18) =1020943a(19) =2792183a(20) =7666358a(21) =21126905a(22) =58422650a(23) =162052566a(24) =450742451a(25) =1256974690a(26) =3513731861a(27) =9843728012a(28) =27633400879a(29) =77721141911