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A117381
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Expansion of 1/((1-4*x*c(x))(1-x^2*c(x))), c(x) the g.f. of A000108.
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1
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1, 4, 21, 109, 575, 3047, 16192, 86171, 458972, 2445825, 13037508, 69509558, 370634265, 1976421031, 10539858413, 56208784808, 299766435277, 1598704176149, 8526238418811, 45472594256564, 242517996824355
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OFFSET
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0,2
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COMMENTS
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Diagonal sums of number triangle A117380.
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LINKS
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FORMULA
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a(n)=sum{k=0..floor(n/2), [k<=n-k]*sum{j=0..n-k, (j/(n-k-j))*C(2n-k-j,n-k-j)[k<=j]*4^(j-k)}}
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CROSSREFS
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KEYWORD
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easy,nonn
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AUTHOR
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STATUS
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approved
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