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A337902
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The number of walks of length 2n+1 on the square lattice that start from the origin (0,0) and end at the vertex (2,1).
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4
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3, 50, 735, 10584, 152460, 2208492, 32207175, 472780880, 6982113996, 103673813880, 1546866469148, 23179817220000, 348690679038000, 5263441096145400, 79698007774092375, 1210159553338375200, 18422202264818467500, 281089726445607849000
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OFFSET
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1,1
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LINKS
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FORMULA
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G.f.: 3*x*3F2(2,5/2,5/2; 3,4; 16*x).
D-finite with recurrence (n-1)*(n+2)*(n+1)*a(n) -4*n*(2*n+1)^2*a(n-1)=0.
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EXAMPLE
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a(1)=3 represents 3 walks of length 3: RRU, URR and RUR.
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CROSSREFS
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KEYWORD
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nonn,easy,walk
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AUTHOR
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STATUS
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approved
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