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1, -2, 7, -36, 246, -2100, 21510, -257040, 3510360, -53933040, 920694600
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listen;
history;
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internal format)
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OFFSET
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0,2
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COMMENTS
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Limiting ratio 2+n*a(n-1)/a(n) converges to A002193.
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LINKS
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FORMULA
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Conjecture: E.g.f.: 2/(2+4*x+x^2) = G(0)/(1+x) where G(k) = 1 - x/((1+x) - x*(1+x)/(x - (1+x)*2/G(k+1) )); (recursively defined continued fraction). - Sergei N. Gladkovskii, Dec 28 2012.
a(n) ~ n! * (-1)^n * (1+sqrt(2))/2 * (1+1/sqrt(2))^n. - Vaclav Kotesovec, Oct 08 2013
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MATHEMATICA
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CoefficientList[Series[2/(2+4*x+x^2), {x, 0, 20}], x]* Range[0, 20]! (* Vaclav Kotesovec, Oct 08 2013 *)
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CROSSREFS
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KEYWORD
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more,sign
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AUTHOR
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STATUS
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approved
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