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A007851
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Number of elements w of the Weyl group D(n) such that the roots sent negative by w span an Abelian subalgebra of the Lie algebra.
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1
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1, 4, 14, 48, 167, 593, 2144, 7864, 29171, 109173, 411501, 1560089, 5943199, 22732739, 87253604, 335897864, 1296447899, 5015206349, 19439895089, 75487384829, 293595204239, 1143532045499, 4459774977449, 17413705988873
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,2
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REFERENCES
| C. K. Fan, A Hecke algebra quotient and some combinatorial applications. J. Algebraic Combin. 5 (1996), no. 3, 175-189.
C. K. Fan, Structure of a Hecke algebra quotient, J. Amer. Math. Soc., 10 (1997), 139-167.
C. K. Fan, Structure of a Hecke algebra quotient, J. Amer. Math. Soc., 10 (1997), 139-167.
J. R. Stembridge, Some combinatorial aspects of reduced words in finite Coxeter groups. Trans. Amer. Math. Soc. 349 (1997), no. 4, 1285-1332.
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FORMULA
| a(n) = (n+3)C(n)/2 - 1, where C(n) is a Catalan number (see A000108).
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CROSSREFS
| Sequence in context: A071757 A082590 A085280 * A014325 A047028 A047138
Adjacent sequences: A007848 A007849 A007850 * A007852 A007853 A007854
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KEYWORD
| nonn,easy
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AUTHOR
| C. Kenneth Fan [ ckfan(AT)MIT.EDU ]
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