Number of unlabeled distributive lattices on n nodes.

Terms

a(0) =1a(1) =1a(2) =1a(3) =1a(4) =2a(5) =3a(6) =5a(7) =8a(8) =15a(9) =26a(10) =47a(11) =82a(12) =151a(13) =269a(14) =494a(15) =891a(16) =1639a(17) =2978a(18) =5483a(19) =10006a(20) =18428a(21) =33749a(22) =62162a(23) =114083a(24) =210189a(25) =386292a(26) =711811a(27) =1309475a(28) =2413144a(29) =4442221