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Search: id:A131105
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| A131105 |
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Rectangular array read by antidiagonals: a(n, k) is the number of ways to put k labeled objects into n labeled boxes so that there are exactly two boxes with exactly one object (n, k >= 2). |
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+0
4
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| 2, 6, 0, 12, 0, 0, 20, 0, 36, 0, 30, 0, 144, 60, 0, 42, 0, 360, 240, 90, 0, 56, 0, 720, 600, 1440, 126, 0, 72, 0, 1260, 1200, 6300, 5544, 168, 0, 90, 0, 2016, 2100, 18000, 26460, 17472, 216, 0, 110, 0, 3024, 3360, 40950, 78120, 136080, 49248, 270, 0, 132, 0, 4320
(list; table; graph; listen)
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OFFSET
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2,1
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COMMENT
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Problem suggested by Brandon Zeidler. Columns 2, 4, and 5 are A002378, 36*A000292, and 60*A000292.
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FORMULA
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a(n, 2) = n^2-n. For k > 2, a(n, k) = sum_{j=1..min(floor(k/2)-1, n-2)} A008299(k-2, j)*n!*(k^2-k)/(2*(n-j-2)!).
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EXAMPLE
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Array begins:
2 0 0 0 0 0
6 0 36 60 90 126
12 0 144 240 1440 5544
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CROSSREFS
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Cf. A131103, A131104, A131106, A131107.
Adjacent sequences: A131102 A131103 A131104 this_sequence A131106 A131107 A131108
Sequence in context: A108431 A019967 A065344 this_sequence A057635 A139717 A138703
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KEYWORD
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easy,nonn,tabl
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AUTHOR
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David Wasserman (dwasserm(AT)earthlink.net), Jun 15 2007
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