Number of 2-sided strip polykites with n cells.

Terms

a(0) =1a(1) =2a(2) =3a(3) =7a(4) =14a(5) =31a(6) =63a(7) =141a(8) =297a(9) =649a(10) =1391a(11) =3026a(12) =6539a(13) =14187a(14) =30619a(15) =66172a(16) =142667a(17) =307883a(18) =663506a(19) =1429816a(20) =3077752a(21) =6622351