Number of 2-sided strip polyrhombs with n cells.

Terms

a(0) =1a(1) =1a(2) =3a(3) =5a(4) =12a(5) =24a(6) =58a(7) =126a(8) =300a(9) =686a(10) =1630a(11) =3792a(12) =8983a(13) =21051a(14) =49776a(15) =116858a(16) =275789a(17) =647573a(18) =1525847a(19) =3580673a(20) =8424978a(21) =19755938a(22) =46426810