Number of fixed hexagonal polyominoes with n cells.

Terms

a(0) =1a(1) =3a(2) =11a(3) =44a(4) =186a(5) =814a(6) =3652a(7) =16689a(8) =77359a(9) =362671a(10) =1716033a(11) =8182213a(12) =39267086a(13) =189492795a(14) =918837374a(15) =4474080844a(16) =21866153748a(17) =107217298977a(18) =527266673134