A181326 Number of columns with an odd sum in all 2-compositions of n. A 2-composition of n is a nonnegative matrix with two rows, such that each column has at least one nonzero entry and whose entries sum up to n.

0, 2, 8, 40, 168, 696, 2776, 10864, 41800, 158816, 597176, 2226512, 8242344, 30328160, 111013784, 404518640, 1468154504, 5309771264, 19143323000, 68823556368, 246805713000, 883028659744, 3152718627672, 11234773009200

Offset: 0

Author

Emeric Deutsch, Oct 13 2010

Keywords

• nonn
• easy

Comments

a(n)=Sum(A181308(n,k), k=0..n).

For the "even sum" case, see A181328.

Examples

			a(2)=8 because in (0/2),(1/1),(2,0),(1,0/0,1),(0,1/1,0),(1,1/0,0), and (0,0/1,1) (the 2-compositions are written as (top row/bottom row)) we have 0+0+0+2+2+2+2=8 columns with odd sums.
		

References

• G. Castiglione, A. Frosini, E. Munarini, A. Restivo and S. Rinaldi, Combinatorial aspects of L-convex polyominoes, European Journal of Combinatorics, 28, 2007, 1724-1741.

Links

• Index entries for linear recurrences with constant coefficients, signature (6,-5,-16,8,8,-4).

Crossrefs

Cf. A181308, A181327, A181328

Programs

Maple

g := 2*z*(1-z)^2/((1+z)^2*(1-4*z+2*z^2)^2): gser := series(g, z = 0, 30): seq(coeff(gser, z, n), n = 0 .. 27);

Formula

G.f. = 2z(1-z)^2/[(1+z)(1-4z+2z^2)]^2.