Number of 2n-bead black-white reversible necklaces with n black beads and fundamental period 2n.

A045628

Number of 2n-bead black-white reversible necklaces with n black beads and fundamental period 2n.

Terms

    a(0) =1a(1) =1a(2) =1a(3) =2a(4) =6a(5) =15a(6) =46a(7) =132a(8) =432a(9) =1384a(10) =4735a(11) =16158a(12) =56766a(13) =200473a(14) =718012a(15) =2587000a(16) =9398080a(17) =34324173a(18) =126067124a(19) =465093570a(20) =1723171550a(21) =6407924165a(22) =23910560070a(23) =89494164972a(24) =335913861648

External references