a(n) is the number of free polyominoes with sprawl n.

Terms

a(0) =1a(1) =0a(2) =0a(3) =0a(4) =0a(5) =1a(6) =0a(7) =0a(8) =1a(9) =0a(10) =1a(11) =1a(12) =3a(13) =2a(14) =4a(15) =6a(16) =13a(17) =15a(18) =30a(19) =50a(20) =93a(21) =158a(22) =287a(23) =513a(24) =950a(25) =1735a(26) =3212a(27) =5945a(28) =11099a(29) =20720