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Search: id:A080721
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| A080721 |
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Triangle of binomial(n,k)*(binomial(n+k,k)-binomial(n+k-2,k-1)). |
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1
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| 1, 1, 1, 1, 4, 4, 1, 9, 21, 14, 1, 16, 66, 100, 50, 1, 25, 160, 410, 455, 182, 1, 36, 330, 1260, 2310, 2016, 672, 1, 49, 609, 3220, 8610, 12222, 8778, 2508, 1, 64, 1036, 7224, 26250, 53592, 61908, 37752, 9438
(list; table; graph; listen)
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OFFSET
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0,5
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COMMENT
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For n>1 and 0 <= k <= n, a(n,k) is the number of compatible k-sets of cluster variables in Fomin and Zelevinsky's 'cluster algebra' of finite type D_n.
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REFERENCES
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S. Fomin and A. Zelevinsky, Cluster algebras I: Foundations, J. Amer. Math. Soc. 15 (2002) no. 2, 497-529.
S. Fomin and A. Zelevinsky, Y-Systems and generalized associahedra, Ann. of Math. (2) 158 (2003), no. 3, 977-1018.
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LINKS
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S. Fomin and A. Zelevinsky, Cluster algebras I: Foundations, J. Amer. Math. Soc. 15 (2002), no. 2, 497-529.
S. Fomin and A. Zelevinsky, Y-systems and generalized associahedra, Ann. of Math. (2) 158 (2003), no. 3, 977-1018.
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CROSSREFS
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Cf. A033282, A063007.
Sequence in context: A128213 A016706 A138679 this_sequence A123588 A106026 A096078
Adjacent sequences: A080718 A080719 A080720 this_sequence A080722 A080723 A080724
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KEYWORD
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easy,nonn,tabl
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AUTHOR
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Paul Boddington (psb(AT)maths.warwick.ac.uk), Mar 07 2003
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