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A253665
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a(n) = 2^n*n!/(floor(n/2)!)^2.
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3
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1, 2, 8, 48, 96, 960, 1280, 17920, 17920, 322560, 258048, 5677056, 3784704, 98402304, 56229888, 1686896640, 843448320, 28677242880, 12745441280, 484326768640, 193730707456, 8136689713152, 2958796259328, 136104627929088, 45368209309696, 2268410465484800
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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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a(2*n) = 4^n*C(2*n, n) = A098430(n).
a(n) = sum(k=0..n, C(n,k)*n!/(floor(n/2)!)^2) = sum(k=0..n, A253666(n,k)).
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MAPLE
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a := n -> 2^n*n!/iquo(n, 2)!^2: seq(a(n), n=0..25);
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MATHEMATICA
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CoefficientList[Series[(1 + 2 (1 - 8 x) x)/(1 - 16 x^2)^(3/2), {x, 0, 20}], x] (* Benedict W. J. Irwin, Aug 15 2016 *)
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PROG
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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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