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 A181290 The sum of the lengths of the 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. The length of the 2-composition is the number of columns. 1
 0, 2, 11, 52, 227, 944, 3800, 14944, 57748, 220128, 829968, 3101376, 11502704, 42393088, 155392768, 566918144, 2059768384, 7456496128, 26905720576, 96804463616, 347386161920, 1243665567744, 4442849839104, 15840448094208 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS a(n)=Sum(k*A181289(n,k), 0<=k<=n). 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(2-z)(1-z)^2/(1-4z+2z^2)^2. MAPLE g := z*(1-z)^2*(2-z)/(1-4*z+2*z^2)^2: gser := series(g, z = 0, 28): seq(coeff(gser, z, n), n = 0 .. 25); CROSSREFS Cf. A181289 Sequence in context: A134963 A026956 A026986 * A026996 A110308 A027201 Adjacent sequences:  A181287 A181288 A181289 * A181291 A181292 A181293 KEYWORD nonn AUTHOR Emeric Deutsch, Oct 12 2010 STATUS approved

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Last modified August 9 02:14 EDT 2020. Contains 336310 sequences. (Running on oeis4.)