Number of fixed polyominoes minus number of free polyominoes for order n.

Terms

a(0) =0a(1) =0a(2) =1a(3) =4a(4) =14a(5) =51a(6) =181a(7) =652a(8) =2356a(9) =8625a(10) =31791a(11) =118195a(12) =442261a(13) =1665299a(14) =6302903a(15) =23968090a(16) =91513682a(17) =350687935a(18) =1348198490a(19) =5198114444a(20) =20094107710a(21) =77860452105a(22) =302340714990