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A115068 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. +0
1
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)
OFFSET

1,2

REFERENCES

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.

FORMULA

T(n,k)=binomial(n,k)*2^(n-k-1)

CROSSREFS

Cf. A007318, A038207.

Adjacent sequences: A115065 A115066 A115067 this_sequence A115069 A115070 A115071

Sequence in context: A143267 A113463 A127718 this_sequence A051495 A073256 A050469

KEYWORD

easy,nonn,tabl

AUTHOR

Elizabeth Morris (epmorris(AT)math.washington.edu), Mar 01 2006

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Last modified October 15 09:18 EDT 2008. Contains 145015 sequences.


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