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A111964
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Expansion of 1/(sqrt(1+4x^2)+x(1-x)).
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1
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1, -1, 0, 1, 1, -4, -1, 11, 2, -35, -1, 112, -9, -369, 66, 1237, -327, -4212, 1433, 14527, -5926, -50659, 23749, 178356, -93427, -633225, 363342, 2264885, -1402803, -8154564, 5390861, 29534183, -20655948, -107538835, 79005679, 393462584, -301884895, -1445937945, 1153012596, 5335046209
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OFFSET
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0,6
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COMMENTS
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Diagonal sums of number triangle A111963.
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LINKS
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FORMULA
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a(n)=sum{k=0..floor(n/2), sum{i=0..floor((n-k)/2), C(2i+2k-n-1, k)C(2i+k-n-1)(-1)^(n-k)*4^i}}
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MATHEMATICA
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CoefficientList[Series[1/(Sqrt[1+4x^2]+x(1-x)), {x, 0, 40}], x] (* Harvey P. Dale, May 27 2012 *)
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CROSSREFS
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KEYWORD
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easy,sign
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AUTHOR
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STATUS
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approved
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