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Search: id:A055663
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| A055663 |
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Number of (3,3; n,n)-partitions of a chain of length n^2+n. |
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+0
1
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| 220, 4004, 43680, 371280, 2713200, 17907120, 109830336, 637408200, 3543239700, 19028509500, 99348849600, 506679132960, 2533395664800, 12454385680800, 60338017584000, 288616850776800, 1365157704174264, 6393385628146440
(list; graph; listen)
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OFFSET
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9,1
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COMMENT
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a (k_1,n_1; k_2,n_2)-partition of a chain C is a chain of k_1+k_2 intervals of C, k_1 being of length n_1 and k_2 of length n_2
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FORMULA
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a(n)=16/3*(2*n-7)*(2*n-9)*(2*n-11)*(2*n-13)*(n-8)*(2*n-15)!/(n*(n-1)*(n-2)*(n-8)!^2)
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EXAMPLE
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a(9)=220 because in the linearly ordered set {1,..,90} we can choose in 220 ways 12 successive blocks, 3 constituted of 3 consecutive elements and 9 of 9 consecutive elements
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CROSSREFS
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Adjacent sequences: A055660 A055661 A055662 this_sequence A055664 A055665 A055666
Sequence in context: A102073 A002025 A027797 this_sequence A022042 A095702 A107506
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KEYWORD
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nonn
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AUTHOR
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Paolo Dominici (pl.dm(AT)libero.it), Jun 07 2000
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