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A020933
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Expansion of (1-4*x)^(21/2).
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1
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1, -42, 798, -9044, 67830, -352716, 1293292, -3325608, 5819814, -6466460, 3879876, -705432, -117572, -54264, -38760, -36176, -40698, -52668, -76076, -120120, -204204, -369512, -705432, -1410864, -2939300, -6348888, -14162904, -32522224, -76659528, -185040240
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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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D-finite with recurrence: n*a(n) +2*(-2*n+23)*a(n-1)=0. - R. J. Mathar, Jan 17 2020
a(n) = (-4)^n*binomial(21/2, n).
Sum_{n>=0} 1/a(n) = 406240/415701 - 46*Pi/(3^13*sqrt(3)).
Sum_{n>=0} (-1)^n/a(n) = 728323714975904/710426513671875 - 92*log(phi)/(5^12*sqrt(5)), where phi is the golden ratio (A001622). (End)
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MATHEMATICA
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CoefficientList[Series[Surd[(1-4x)^21, 2], {x, 0, 30}], x] (* Harvey P. Dale, Feb 25 2020 *)
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CROSSREFS
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Cf. A001622, A002420, A002421, A002422, A002423, A002424, A020923, A020925, A020927, A020929, A020931.
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KEYWORD
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sign
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AUTHOR
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STATUS
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approved
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