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Search: id:A002047
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| A002047 |
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Number of 3 X (2n+1) zero-sum arrays.
(Formerly M1688 N0666)
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+0
1
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| 1, 2, 6, 28, 244, 2544, 35600, 659632, 15106128, 425802176
(list; graph; listen)
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OFFSET
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0,2
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COMMENT
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This can be interpreted as the number of ways to choose 2n+1 cells in a hexagonal grid of side n+1 such that no two are in the same row or left diagonal or right diagonal. - Alex Fink (a00(AT)shaw.ca), Mar 16 2005
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REFERENCES
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B. T. Bennett and R. B. Potts, Arrays and brooks, J. Austral. Math. Soc., 7 (1967), 23-31.
A. Kotzig and P. J. Laufer, When are permutations additive?, Amer. Math. Monthly, 85 (1978), 364-365.
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LINKS
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C. Bebeacua, T. Mansour, A. Postnikov and S. Severini, On the x-rays of permutations
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EXAMPLE
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a(2) = 6 corresponds to
..O.X.X.......X.X.O.......O.X.X.......X.O.X.......X.O.X.......X.X.O
.X.X.O.X.....X.O.X.X.....X.X.X.O.....X.X.X.O.....O.X.X.X.....O.X.X.X
X.X.X.X.O...O.X.X.X.X...X.O.X.X.X...O.X.X.X.X...X.X.X.X.O...X.X.X.O.X
.O.X.X.X.....X.X.X.O.....X.X.X.O.....X.O.X.X.....X.X.O.X.....O.X.X.X
..X.O.X.......X.O.X.......O.X.X.......X.X.O.......O.X.X.......X.X.O
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CROSSREFS
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Sequence in context: A006117 A118025 A119966 this_sequence A126340 A136639 A027109
Adjacent sequences: A002044 A002045 A002046 this_sequence A002048 A002049 A002050
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KEYWORD
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nonn,nice
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AUTHOR
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njas
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EXTENSIONS
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More terms from Alex Fink (a00(AT)shaw.ca), Mar 16 2005
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