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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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2
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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
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,3
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COMMENTS
| a(n)=A121748(n,0).
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REFERENCES
| 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
| 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
| 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
| 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
| Cf. A121746, A121748.
Sequence in context: A121753 A173994 A150032 * A009386 A009605 A009681
Adjacent sequences: A121746 A121747 A121748 * A121750 A121751 A121752
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KEYWORD
| nonn
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AUTHOR
| Emeric Deutsch (deutsch(AT)duke.poly.edu), Aug 20 2006
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