Number of 2-sided strip polycairos with n cells.

Terms

a(0) =1a(1) =2a(2) =4a(3) =10a(4) =25a(5) =64a(6) =158a(7) =405a(8) =1018a(9) =2580a(10) =6512a(11) =16435a(12) =41411a(13) =104280a(14) =262161a(15) =658763a(16) =1652954a(17) =4145802a(18) =10386103