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A292934
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E.g.f.: x^2/(x+3-2*exp(x)).
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2
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0, 0, 2, 6, 48, 400, 4140, 49644, 681296, 10515600, 180349380, 3402380740, 70023004920, 1561206957336, 37485640585484, 964345394431020, 26462386594676640, 771532717446066208, 23817889096309943892, 776127882633846005268
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OFFSET
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0,3
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COMMENTS
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Number of associative and quasitrivial binary operations on {1,...,n} that have both neutral and annihilator elements.
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LINKS
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FORMULA
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a(n) ~ n! / ((r-1) * (r-3)^(n-1)), where r = -LambertW(-1, -2*exp(-3)) = 3.5830738760366909976807989989303134394318270218566... - Vaclav Kotesovec, Sep 27 2017
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CROSSREFS
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KEYWORD
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nonn,easy
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AUTHOR
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STATUS
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approved
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