Number of 1-sided strip polyrhombs with n cells.

Terms

a(0) =1a(1) =2a(2) =4a(3) =10a(4) =20a(5) =48a(6) =106a(7) =252a(8) =578a(9) =1372a(10) =3208a(11) =7584a(12) =17850a(13) =42102a(14) =99276a(15) =233716a(16) =550960a(17) =1295146a(18) =3050226a(19) =7161346a(20) =16846668a(21) =39511876a(22) =92845830