a(n) is the number of complement pairs of imprimitive (periodic) 2n-bead balanced binary necklaces.

Terms

a(0) =0a(1) =0a(2) =0a(3) =0a(4) =0a(5) =0a(6) =1a(7) =0a(8) =3a(9) =1a(10) =11a(11) =0a(12) =39a(13) =0a(14) =118a(15) =12a(16) =395a(17) =0a(18) =1372a(19) =0a(20) =4601a(21) =119a(22) =15986a(23) =0a(24) =56662a(25) =11a(26) =199854a(27) =1337a(28) =716135a(29) =0