Number of open binary words of length n.

Terms

a(0) =0a(1) =0a(2) =2a(3) =4a(4) =10a(5) =20a(6) =44a(7) =92a(8) =194a(9) =396a(10) =820a(11) =1684a(12) =3432a(13) =6972a(14) =14144a(15) =28636a(16) =57890a(17) =116828a(18) =235500a(19) =474304a(20) =954444a(21) =1919364a(22) =3857548a(23) =7748888a(24) =15558988a(25) =31229384a(26) =62662088a(27) =125696800a(28) =252079196a(29) =505423476