Number of chiral pairs of polyomino rings of length 4n with fourfold rotational symmetry.

Terms

a(0) =0a(1) =0a(2) =0a(3) =0a(4) =1a(5) =2a(6) =6a(7) =12a(8) =29a(9) =61a(10) =138a(11) =294a(12) =649a(13) =1402a(14) =3073a(15) =6696a(16) =14676a(17) =32199a(18) =70764a(19) =156062a(20) =344209a(21) =762433a(22) =1687745a(23) =3751845a(24) =8333371a(25) =18582147a(26) =41399110a(27) =92557961a(28) =206765077a(29) =463343343