Number of simple 2n-gons with only right angles, disregarding edge lengths.

Terms

a(0) =0a(1) =1a(2) =1a(3) =4a(4) =8a(5) =29a(6) =79a(7) =280a(8) =912a(9) =3260a(10) =11410a(11) =41272a(12) =148976a(13) =544802a(14) =1997499a(15) =7372080a(16) =27299360a(17) =101520714a(18) =378721134a(19) =1417339352a(20) =5318837680a(21) =20012141478a(22) =75473438326a(23) =285268537424