Number of n-bead black-white reversible strings with fundamental period n.

Terms

a(0) =1a(1) =2a(2) =1a(3) =4a(4) =7a(5) =18a(6) =29a(7) =70a(8) =126a(9) =266a(10) =507a(11) =1054a(12) =2037a(13) =4158a(14) =8183a(15) =16488a(16) =32760a(17) =65790a(18) =131026a(19) =262654a(20) =524265a(21) =1049524a(22) =2097119a(23) =4196350a(24) =8388450a(25) =16781292a(26) =33554367a(27) =67116784a(28) =134217657a(29) =268451838