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A025239
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a(n) = a(1)*a(n-1) + a(2)*a(n-2) + ...+ a(n-2)*a(2) for n >= 3.
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1
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2, 3, 6, 21, 78, 318, 1356, 5997, 27222, 126138, 594132, 2836290, 13692300, 66729180, 327855768, 1622216829, 8076311142, 40427919714, 203353800324, 1027318915254, 5210182030308, 26517609163812, 135397544040744, 693364054299474
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OFFSET
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1,1
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LINKS
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FORMULA
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Recurrence (for n>3): n*a(n) = 2*(2*n-3)*a(n-1) + 8*(n-3)*a(n-2). - Vaclav Kotesovec, Oct 07 2012
a(n) ~ sqrt(3-sqrt(3))*(2+2*sqrt(3))^n/(4*sqrt(Pi)*n^(3/2)). - Vaclav Kotesovec, Oct 07 2012
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MATHEMATICA
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Join[{2}, Drop[CoefficientList[Series[(1-Sqrt[1-4x-8x^2])/2, {x, 0, 30}], x], 2]] (* Harvey P. Dale, Nov 05 2011 *)
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PROG
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(PARI) a(n)=polcoeff((1-sqrt(1-4*x-8*x^2+x*O(x^n)))/2, n)
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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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