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A026306
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a(n) = T(2n,n+1), where T is the array in A026300.
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0
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0, 2, 12, 69, 392, 2235, 12804, 73710, 426192, 2473704, 14405800, 84137130, 492652824, 2891110235, 16999928820, 100136858625, 590778928800, 3490370847876, 20647839813048, 122287764072938, 725023671281520, 4302720916638417
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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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g.f. A(x)=(1/B(x))'-1, where B(x) g.f. of A006605.
a(n) = n*(Sum_{j=0..2*n+1} binomial(j,-3*n+2*j-1)*binomial(2*n+1,j)))/(2*n+1) - Vladimir Kruchinin, May 15 2014
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EXAMPLE
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G.f. = 2*x + 12*x^2 + 69*x^3 + 392*x^4 + 2235*x^5 + 12804*x^6 + 73710*x^7 + ...
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PROG
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(Maxima)
a(n):=(n*sum(binomial(j, -3*n+2*j-1)*binomial(2*n+1, j), j, 0, 2*n+1))/(2*n+1); Vladimir Kruchinin, May 15 2014
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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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