Number of column convex polyominoes with n hexagonal cells.

Terms

a(0) =1a(1) =3a(2) =11a(3) =42a(4) =162a(5) =626a(6) =2419a(7) =9346a(8) =36106a(9) =139483a(10) =538841a(11) =2081612a(12) =8041537a(13) =31065506a(14) =120010109a(15) =463614741a(16) =1791004361a(17) =6918884013a(18) =26728553546a(19) =103255896932a(20) =398891029862