Number of closed binary words of length n.

Terms

a(0) =1a(1) =2a(2) =2a(3) =4a(4) =6a(5) =12a(6) =20a(7) =36a(8) =62a(9) =116a(10) =204a(11) =364a(12) =664a(13) =1220a(14) =2240a(15) =4132a(16) =7646a(17) =14244a(18) =26644a(19) =49984a(20) =94132a(21) =177788a(22) =336756a(23) =639720a(24) =1218228a(25) =2325048a(26) =4446776a(27) =8520928a(28) =16356260a(29) =31447436