Number of achiral hexagonal polyominoes with n cells.

Terms

a(0) =1a(1) =1a(2) =3a(3) =4a(4) =11a(5) =17a(6) =46a(7) =75a(8) =202a(9) =341a(10) =914a(11) =1581a(12) =4222a(13) =7436a(14) =19794a(15) =35357a(16) =93859a(17) =169558a(18) =449039a(19) =818793a(20) =2163827a(21) =3976636a(22) =10489341a(23) =19406704a(24) =51103471a(25) =95099113a(26) =250040802a(27) =467679257a(28) =1227941119a(29) =2307128946