Number of self-complementary 2-colored bracelets (turnover necklaces) with 2n beads.

Terms

a(0) =1a(1) =2a(2) =3a(3) =6a(4) =10a(5) =20a(6) =37a(7) =74a(8) =143a(9) =284a(10) =559a(11) =1114a(12) =2206a(13) =4394a(14) =8740a(15) =17418a(16) =34696a(17) =69194a(18) =137971a(19) =275280a(20) =549258a(21) =1096286a(22) =2188333a(23) =4369162a(24) =8724154a(25) =17422652a(26) =34797199a(27) =69505908a(28) =138845926a(29) =277383872