a(n) is the number of unlabeled planar modular lattices on n nodes.

Terms

a(0) =1a(1) =1a(2) =1a(3) =2a(4) =4a(5) =8a(6) =16a(7) =33a(8) =70a(9) =151a(10) =329a(11) =723a(12) =1601a(13) =3569a(14) =8000a(15) =18015a(16) =40723a(17) =92351a(18) =209997a(19) =478598a(20) =1092856a(21) =2499567a(22) =5724970a(23) =13128115a(24) =30135636a(25) =69238343a(26) =159202607a(27) =366308948a(28) =843338278a(29) =1942591448