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Search: id:A121695
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| A121695 |
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Number of odd-length first columns in 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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| 1, 1, 3, 15, 57, 423, 2457, 22743, 178857, 1998423, 19774377, 259643223, 3093367977, 46722798423, 650703531177, 11118365780823, 177186743211177, 3379687537748823, 60644049519531177, 1277452054977620823
(list; graph; listen)
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OFFSET
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1,3
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COMMENT
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a(n)+A121696(n)=n!
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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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a(n)=a(n-2)+(n-2)!(n*floor(n/2)-1) for n>=3; a(1)=a(2)=1.
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MAPLE
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a[1]:=1: a[2]:=1: for n from 3 to 23 do a[n]:=a[n-2]+(n-2)!*(n*floor(n/2)-1) od: seq(a[n], n=1..23);
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CROSSREFS
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Cf. A121696.
Adjacent sequences: A121692 A121693 A121694 this_sequence A121696 A121697 A121698
Sequence in context: A118048 A125673 A123007 this_sequence A017949 A049178 A049150
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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 17 2006
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