A208722 - OEIS

%I #10 Mar 19 2017 01:11:42

%S 0,1,4,15,52,210,796,3175,12468,49288,194140,766110,3019224,11905330,

%T 46938192,185111095,730148332,2880799554,11369141308,44881708072,

%U 177229210656,700047776214,2765947680124,10931565973950,43215517211240,170888480306500

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

%H Andrew Howroyd, <a href="/A208722/b208722.txt">Table of n, a(n) for n = 1..100</a>

%e All solutions for n=4:

%e ..1....1....3....2....1....2....2....2....2....1....1....1....1....1....1

%e ..2....2....4....3....2....3....3....3....3....2....2....2....2....2....2

%e ..1....3....3....2....3....2....4....4....2....3....1....1....3....3....1

%e ..2....4....4....3....2....3....3....3....3....2....2....2....4....2....2

%e ..3....3....3....2....1....2....4....2....4....3....1....3....3....3....1

%e ..2....4....4....3....2....3....3....3....3....4....2....4....2....2....2

%e ..3....3....3....2....3....4....4....4....4....3....1....3....3....3....3

%e ..2....2....4....3....2....3....3....3....3....2....2....2....2....2....2

%Y Diagonal of A208727.

%K nonn

%O 1,3

%A _R. H. Hardin_, Mar 01 2012

%E a(13)-a(26) from _Andrew Howroyd_, Mar 18 2017