Number of binary necklaces of 2n beads for which a cut exists producing a palindrome.

Terms

a(0) =2a(1) =3a(2) =6a(3) =9a(4) =20a(5) =34a(6) =72a(7) =129a(8) =272a(9) =516a(10) =1056a(11) =2050a(12) =4160a(13) =8200a(14) =16512a(15) =32769a(16) =65792a(17) =131088a(18) =262656a(19) =524292a(20) =1049600a(21) =2097184a(22) =4196352a(23) =8388610a(24) =16781312a(25) =33554496a(26) =67117056a(27) =134217736a(28) =268451840a(29) =536871040