A199697 Number of -1..1 arrays x(0..n-1) of n elements with zero sum and no two neighbors equal.

1, 2, 6, 8, 14, 32, 56, 100, 204, 388, 722, 1416, 2750, 5256, 10222, 19944, 38650, 75272, 147142, 287120, 561018, 1098752, 2152092, 4217620, 8276376, 16250292, 31921374, 62754072, 123440514, 242921784, 478310952, 942260548, 1856994908, 3661288036

Offset: 1

Author

R. H. Hardin, Nov 09 2011

Keywords

• nonn

Comments

Column 1 of A199704

Examples

			All solutions for n=5
..0...-1....1...-1....1...-1...-1....0....1...-1....0....1....1....0
.-1....1...-1....1....0....1....0...-1...-1....1....1...-1...-1....1
..1....0....0...-1...-1...-1....1....0....1....0....0....1....0...-1
.-1...-1....1....1....1....0...-1....1....0....1...-1...-1...-1....1
..1....1...-1....0...-1....1....1....0...-1...-1....0....0....1...-1
		

Links

• R. H. Hardin, Table of n, a(n) for n = 1..200

Programs

Mathematica

Rest@ CoefficientList[Series[((x + 1)^2*Sqrt[(1 - x)/(1 - x - 4*x^3)] - 2 x - 1)/x, {x, 0, 34}], x] (* Michael De Vlieger, Mar 08 2017 *)

Formula

G.f.: ((x+1)^2*sqrt((1-x)/(1-x-4*x^3))-2*x-1)/x. - Stefan Hollos, Mar 08 2017