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A371617
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G.f. satisfies A(x) = ( 1 + x / (1 - x*A(x)^3)^3 )^2.
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3
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1, 2, 7, 54, 419, 3644, 33366, 317672, 3113559, 31200060, 318219653, 3292546660, 34475311605, 364621943538, 3889561661610, 41799988930926, 452126713579192, 4918321519144206, 53773399008883695, 590578523863692086, 6512515698908748358
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OFFSET
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0,2
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LINKS
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FORMULA
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a(n) = Sum_{k=0..n} binomial(6*(n-k)+2,k) * binomial(n+2*k-1,n-k)/(3*(n-k)+1).
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PROG
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(PARI) a(n, r=2, s=3, t=0, u=6) = r*sum(k=0, n, binomial(t*k+u*(n-k)+r, k)*binomial(n+(s-1)*k-1, n-k)/(t*k+u*(n-k)+r));
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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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