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Search: id:A121749
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| A121749 |
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Number of deco polyominoes of height n, consisting only of columns of odd length. 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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3
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| 1, 1, 2, 6, 16, 66, 246, 1248, 5976, 36120, 210480, 1479600, 10140480, 81340560, 640367280, 5773662720, 51312240000, 513773124480, 5085768280320, 55995414048000, 610811823283200, 7334879610643200, 87402605773190400
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OFFSET
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1,3
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COMMENT
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a(n)=A121748(n,0).
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REFERENCES
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E. Barcucci, S. Brunetti and F. Del Ristoro, Succession rules and deco polyominoes, Theoret. Informatics Appl., 34, 2000, 1-14.
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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Recurrence relation: a(n)=floor(n/2)(a(n-1)+a(n-2)) for n>=3, a(1)=a(2)=1.
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EXAMPLE
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a(2)=1 because the deco polyominoes of height 2 are the vertical and horizontal dominoes and only the horizontal one consists only of columns of odd length.
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MAPLE
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a[1]:=1: a[2]:=1: for n from 3 to 26 do a[n]:=floor(n/2)*(a[n-1]+a[n-2]) od: seq(a[n], n=1..26);
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CROSSREFS
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Cf. A121746, A121748.
Sequence in context: A150031 A121753 A150032 this_sequence A009386 A009605 A009681
Adjacent sequences: A121746 A121747 A121748 this_sequence A121750 A121751 A121752
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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), Aug 20 2006
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