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 A181300 Number of columns with top entry equal to bottom entry in all 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. 1
 0, 0, 1, 4, 19, 80, 328, 1304, 5084, 19512, 73976, 277688, 1033848, 3822584, 14050824, 51385720, 187095240, 678570360, 2452626312, 8837584248, 31756892552, 113831195000, 407102551688, 1452956457336, 5175872174728 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,4 COMMENTS a(n)=Sum(k*A181299(n,k),k>=0). 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*(1-z)^3/[(1+z)(1-4z+2z^2)^2]. MAPLE g := z^2*(1-z)^3/((1+z)*(1-4*z+2*z^2)^2): gser := series(g, z = 0, 30): seq(coeff(gser, z, n), n = 0 .. 27); CROSSREFS Cf. A181299 Sequence in context: A320088 A122909 A215037 * A027240 A050914 A017961 Adjacent sequences:  A181297 A181298 A181299 * A181301 A181302 A181303 KEYWORD nonn AUTHOR Emeric Deutsch, Oct 12 2010 STATUS approved

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Last modified August 22 07:17 EDT 2019. Contains 326172 sequences. (Running on oeis4.)