Number of free poly-[3^4.6]-tiles (holes allowed) with n cells.

Terms

a(0) =1a(1) =3a(2) =8a(3) =25a(4) =80a(5) =291a(6) =1036a(7) =3875a(8) =14561a(9) =55624a(10) =213951a(11) =830712a(12) =3244355a(13) =12747718a(14) =50320659a(15) =199491045a(16) =793754027a(17) =3168756843a(18) =12687184463a(19) =50932363171