Number of 2n-bead necklaces labeled with numbers 1..n not allowing reversal, with neighbors differing by exactly 1.

A208722

Number of 2n-bead necklaces labeled with numbers 1..n not allowing reversal, with neighbors differing by exactly 1.

Terms

    a(0) =0a(1) =1a(2) =4a(3) =15a(4) =52a(5) =210a(6) =796a(7) =3175a(8) =12468a(9) =49288a(10) =194140a(11) =766110a(12) =3019224a(13) =11905330a(14) =46938192a(15) =185111095a(16) =730148332a(17) =2880799554a(18) =11369141308a(19) =44881708072a(20) =177229210656a(21) =700047776214

External references