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Search: id:A051743
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| A051743 |
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a(n)=(1/24)*n*(n+5)*(n^2+n+6). |
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+0
3
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| 2, 7, 18, 39, 75, 132, 217, 338, 504, 725, 1012, 1377, 1833, 2394, 3075, 3892, 4862, 6003, 7334, 8875, 10647, 12672, 14973, 17574, 20500, 23777, 27432, 31493, 35989, 40950, 46407, 52392, 58938, 66079, 73850, 82287, 91427, 101308, 111969, 123450
(list; graph; listen)
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OFFSET
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1,1
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COMMENT
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This is exactly the number of directed column-convex polyominoes
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FORMULA
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a(n)=binomial(n+3, n-1) + binomial(n, n-1) = binomial(n+3, 4) + binomial(n, 1), n > 0.
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CROSSREFS
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Cf. A005435, A006027, A105450.
Adjacent sequences: A051740 A051741 A051742 this_sequence A051744 A051745 A051746
Sequence in context: A141631 A077131 A086741 this_sequence A054111 A055503 A077802
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KEYWORD
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easy,nonn
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AUTHOR
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Klaus Strassburger (strass(AT)ddfi.uni-duesseldorf.de), Dec 07 1999
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