Number of one-sided hexagonal polyominoes with n cells.

Terms

a(0) =1a(1) =1a(2) =3a(3) =10a(4) =33a(5) =147a(6) =620a(7) =2821a(8) =12942a(9) =60639a(10) =286190a(11) =1364621a(12) =6545430a(13) =31586358a(14) =153143956a(15) =745700845a(16) =3644379397a(17) =17869651166a(18) =87877879487a(19) =433301253231