Number of directed animals of size n (or directed n-ominoes in standard position).

Terms

a(0) =1a(1) =1a(2) =2a(3) =5a(4) =13a(5) =35a(6) =96a(7) =267a(8) =750a(9) =2123a(10) =6046a(11) =17303a(12) =49721a(13) =143365a(14) =414584a(15) =1201917a(16) =3492117a(17) =10165779a(18) =29643870a(19) =86574831a(20) =253188111a(21) =741365049a(22) =2173243128a(23) =6377181825a(24) =18730782252a(25) =55062586341a(26) =161995031226a(27) =476941691177