Free polyominoes with 2n squares, having 180-degree rotational symmetry about a square mid-side, but no reflective symmetry.

A234008

Free polyominoes with 2n squares, having 180-degree rotational symmetry about a square mid-side, but no reflective symmetry.

Terms

    a(0) =0a(1) =1a(2) =4a(3) =16a(4) =60a(5) =231a(6) =877a(7) =3362a(8) =12905a(9) =49825a(10) =193003a(11) =750581a(12) =2927792a(13) =11453171a(14) =44911853a(15) =176499605a(16) =694954416a(17) =2741031257a(18) =10827727980a(19) =42831355495a(20) =169640762209a(21) =672657218163

External references