Number of rotationally symmetric polyominoes with n cells (that is, polyominoes with exactly the symmetry group C_2 generated by a 180-degree rotation).

A006747

Number of rotationally symmetric polyominoes with n cells (that is, polyominoes with exactly the symmetry group C_2 generated by a 180-degree rotation).

Terms

    a(0) =0a(1) =0a(2) =0a(3) =1a(4) =1a(5) =5a(6) =4a(7) =18a(8) =19a(9) =73a(10) =73a(11) =278a(12) =283a(13) =1076a(14) =1090a(15) =4125a(16) =4183a(17) =15939a(18) =16105a(19) =61628a(20) =62170a(21) =239388a(22) =240907a(23) =932230a(24) =936447a(25) =3641945a(26) =3651618a(27) =14262540a(28) =14277519a(29) =55987858

External references