Number of 2n-bead necklaces labeled with numbers 1..n allowing reversal, with neighbors differing by exactly 1.

A208666

Number of 2n-bead necklaces labeled with numbers 1..n allowing reversal, with neighbors differing by exactly 1.

Terms

    a(0) =0a(1) =1a(2) =4a(3) =14a(4) =44a(5) =152a(6) =514a(7) =1866a(8) =6884a(9) =26137a(10) =100442a(11) =390592a(12) =1526272a(13) =5989223a(14) =23548688a(15) =92727898a(16) =365445200a(17) =1441195226a(18) =5686268314a(19) =22444465311a(20) =88622259788a(21) =350040069245

External references