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 A181337 Number of even entries in the top rows of 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. 2
 0, 1, 6, 28, 123, 512, 2064, 8124, 31416, 119820, 451972, 1689532, 6268276, 23107836, 84721796, 309151932, 1123431812, 4067533244, 14679173444, 52821023932, 189571527236, 678748381372, 2424976195396, 8646702275772 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 COMMENTS a(n)=Sum(A181336(n,k), k=0..n). For the case of the odd entries see A181336. 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 FORMULA G.f. = z(1+z-z^2)(1-z)^2/[(1+z)(1-4z+2z^2)^2]. EXAMPLE a(2)=6 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 1+0+1+1+1+0+2=6 even entries. MAPLE g := z*(1-z)^2*(1+z-z^2)/((1+z)*(1-4*z+2*z^2)^2): gser := series(g, z = 0, 28): seq(coeff(gser, z, n), n = 0 .. 25); CROSSREFS Cf. A181305, A181336. Sequence in context: A026851 A267689 A300996 * A002693 A289779 A117423 Adjacent sequences:  A181334 A181335 A181336 * A181338 A181339 A181340 KEYWORD nonn AUTHOR Emeric Deutsch, Oct 14 2010 STATUS approved

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Last modified September 18 12:29 EDT 2019. Contains 327170 sequences. (Running on oeis4.)