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A112520
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Expansion of 2/(3-sqrt(3-2*sqrt(1-4x))).
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1
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1, 1, 1, 3, 6, 21, 54, 195, 573, 2086, 6646, 24289, 81540, 299136, 1040262, 3832923, 13660698, 50572983, 183450064, 682447378, 2507959846, 9374078232, 34791088014, 130624080993, 488542321116, 1841890385196, 6931198308924
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OFFSET
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0,4
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COMMENTS
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Row sums of number triangle A112519.
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LINKS
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FORMULA
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a(n)=sum{k=0..n, sum{j=0..n, (k/n)(-1)^(j-k)C(2n-j-1, n-j)C(2j-k-1, j-k)}}.
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MATHEMATICA
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CoefficientList[Series[2/(3-Sqrt[3-2*Sqrt[1-4x]]), {x, 0, 30}], x] (* Harvey P. Dale, Nov 28 2016 *)
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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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