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Search: id:A134437
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| A134437 |
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Number of cells in the 2nd rows of all deco polyominoes of height n. A deco polyomino is a directed column-convex polyomino in which the height, measured along the diagonal, is attained only in the last column. |
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+0
2
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| 0, 1, 7, 45, 312, 2400, 20520, 194040, 2016000, 22861440, 281232000, 3732220800, 53169177600, 809512704000, 13120332825600, 225573828480000, 4100866818048000, 78606921609216000
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OFFSET
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1,3
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COMMENT
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a(n)=Sum(k*A134436(n,k),k=0..n-1).
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REFERENCES
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E. Barcucci, A. del Lungo, and R. Pinzani, "Deco" polyominoes, permutations and random generation, Theoretical Computer Science, 159, 1996, 29-42.
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FORMULA
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a(n)=(1/4)(3n-2)(n-1)(n-1)! Rec. rel.: a(n)=(1/2)(3n-4)(n-1)! + (n-1)a(n-1); a(1)=0.
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EXAMPLE
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a(2)=1 because the horizontal domino has no cells in the 2nd row and the vertical domino has 1 cell in the 2nd row.
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MAPLE
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seq((1/4)*(3*n-2)*(n-1)*factorial(n-1), n = 1 .. 18)
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CROSSREFS
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Cf. A134436.
Adjacent sequences: A134434 A134435 A134436 this_sequence A134438 A134439 A134440
Sequence in context: A062274 A143835 A103719 this_sequence A018927 A001266 A071971
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KEYWORD
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nonn
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AUTHOR
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Emeric Deutsch (deutsch(AT)duke.poly.edu), Nov 30 2007
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