Number of lattices on n unlabeled nodes.

Terms

a(0) =1a(1) =1a(2) =1a(3) =1a(4) =2a(5) =5a(6) =15a(7) =53a(8) =222a(9) =1078a(10) =5994a(11) =37622a(12) =262776a(13) =2018305a(14) =16873364a(15) =152233518a(16) =1471613387a(17) =15150569446a(18) =165269824761