Number of achiral polyominoes with n cells.

Terms

a(0) =1a(1) =1a(2) =1a(3) =2a(4) =3a(5) =6a(6) =10a(7) =20a(8) =34a(9) =70a(10) =121a(11) =250a(12) =441a(13) =912a(14) =1630a(15) =3375a(16) =6092a(17) =12624a(18) =22961a(19) =47616a(20) =87136a(21) =180811a(22) =332549a(23) =690398a(24) =1275166a(25) =2648422a(26) =4909364a(27) =10199792a(28) =18966700a(29) =39416488