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A366200
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G.f. A(x) satisfies A(x) = 1 + x*(1 + x)^3*A(x)^3.
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3
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1, 1, 6, 33, 209, 1425, 10206, 75751, 577494, 4495368, 35582439, 285524184, 2317387098, 18990744137, 156918815760, 1305927563487, 10936673012579, 92098612059051, 779391530714589, 6624730079900931, 56532669993156696, 484156547579505717, 4159926573597719575
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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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a(n) = Sum_{k=0..n} binomial(3*k,n-k) * binomial(3*k,k)/(2*k+1).
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PROG
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(PARI) a(n) = sum(k=0, n, binomial(3*k, n-k)*binomial(3*k, k)/(2*k+1));
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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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