Number of imprimitive (periodic) 2n-bead black-white complementable necklaces with n black beads.

Terms

a(0) =0a(1) =0a(2) =1a(3) =1a(4) =2a(5) =1a(6) =4a(7) =1a(8) =7a(9) =3a(10) =16a(11) =1a(12) =49a(13) =1a(14) =129a(15) =17a(16) =415a(17) =1a(18) =1408a(19) =1a(20) =4659a(21) =130a(22) =16081a(23) =1a(24) =56858a(25) =15a(26) =200171a(27) =1367a(28) =716733a(29) =1