cp's OEIS Frontend

A208666 Number of 2n-bead necklaces labeled with numbers 1..n allowing reversal, with neighbors differing by exactly 1.

%I A208666 #14 Mar 20 2017 09:49:59
%S A208666 0,1,4,14,44,152,514,1866,6884,26137,100442,390592,1526272,5989223,
%T A208666 23548688,92727898,365445200,1441195226,5686268314,22444465311,
%U A208666 88622259788,350040069245,1383007946774,5465854718664,21607909105528,85444555330132,337962745845558,1337094537703089
%N A208666 Number of 2n-bead necklaces labeled with numbers 1..n allowing reversal, with neighbors differing by exactly 1.
%H A208666 Andrew Howroyd, <a href="/A208666/b208666.txt">Table of n, a(n) for n = 1..100</a>
%F A208666 a(n) = (2*A208722(n) + A220062(n+1,n))/4. - _Andrew Howroyd_, Mar 19 2017
%e A208666 All solutions for n=3:
%e A208666 ..1....1....1....2
%e A208666 ..2....2....2....3
%e A208666 ..1....3....1....2
%e A208666 ..2....2....2....3
%e A208666 ..3....3....1....2
%e A208666 ..2....2....2....3
%Y A208666 Diagonal of A208671.
%K A208666 nonn
%O A208666 1,3
%A A208666 _R. H. Hardin_, Feb 29 2012
%E A208666 a(11)-a(28) from _Andrew Howroyd_, Mar 19 2017