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A289451
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Related to number of mesh patterns of length 2 that avoid the pattern 231.
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0
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1, 1, 1, 2, 8, 32, 117, 408, 1402, 4826, 16751
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history;
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OFFSET
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1,4
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LINKS
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FORMULA
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a(n) = binomial(2*n,n)/(n+1) - (n-1)*n/2.
G.f.: (1-sqrt(1-4*x))/(2*x) - x^2/((1-x))^3. (End)
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CROSSREFS
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KEYWORD
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nonn,more
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AUTHOR
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STATUS
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approved
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