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Search: id:A115068
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| A115068 |
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Triangle read by rows: T(n,k) = number of elements in the Coxeter group D_n with descent set contained in {s_k}, for 0<=k<=n-1. |
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+0
1
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| 1, 2, 2, 4, 6, 3, 8, 16, 12, 4, 16, 40, 40, 20, 5, 32, 96, 120, 80, 30, 6, 64, 224, 336, 280, 140, 42, 7, 128, 512, 896, 896, 560, 224, 56, 8, 256, 1152, 2304, 2688, 2016, 1008, 336, 72, 9, 512, 2560, 5760, 7680, 6720, 4032, 1680, 480, 90, 10, 1024, 5632, 14080, 21120
(list; table; graph; listen)
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OFFSET
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1,2
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REFERENCES
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A. Bjorner and F. Brenti, Combinatorics of Coxeter Groups, Springer, New York, 2005.
J. E. Humphreys, Reflection Groups and Coxeter Groups, Cambridge University Press, Cambridge, 1990.
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FORMULA
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T(n,k)=binomial(n,k)*2^(n-k-1)
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CROSSREFS
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Cf. A007318, A038207.
Sequence in context: A143267 A113463 A127718 this_sequence A051495 A073256 A166362
Adjacent sequences: A115065 A115066 A115067 this_sequence A115069 A115070 A115071
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KEYWORD
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easy,nonn,tabl
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AUTHOR
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Elizabeth Morris (epmorris(AT)math.washington.edu), Mar 01 2006
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