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A241805
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Number of ballot sequences of length 2n+1 having exactly n descents.
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2
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1, 1, 3, 17, 146, 1615, 21895, 349021, 6385041, 131722015, 3019039806, 76052414727, 2087753039823, 61995921313948, 1979138443335708, 67572818967182165, 2456489615222703765, 94710044795486692712, 3859301582400404494533, 165700769713109075755060
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OFFSET
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0,3
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LINKS
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FORMULA
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EXAMPLE
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a(1) = 1: [1,2,1].
a(2) = 3: [1,2,1,2,1], [1,2,1,3,1], [1,2,1,3,2].
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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