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

Terms

a(0) =1a(1) =1a(2) =1a(3) =1a(4) =2a(5) =4a(6) =8a(7) =16a(8) =34a(9) =72a(10) =157a(11) =343a(12) =766a(13) =1718a(14) =3899a(15) =8898a(16) =20475a(17) =47321a(18) =110024a(19) =256791a(20) =601991a(21) =1415768a(22) =3340847a(23) =7904700a(24) =18752943a(25) =44588803a(26) =106247120a(27) =253644319a(28) =606603025a(29) =1453029516