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A121797
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Number of dissimilar forests on n nodes.
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1
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1, 1, 1, 3, 7, 21, 63, 203, 655, 2225, 7519, 26279, 91601, 326873, 1162873, 4215645, 15229413, 55842223, 204204265, 755626769, 2788876167, 10398436275, 38671589327, 145061791275, 542955212801, 2047149292105, 7702710310237
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OFFSET
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0,4
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LINKS
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FORMULA
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G.f.: Product_{n=1..infinity} (1+T_n x^n), where T_n (A000108) has g.f. (1-sqrt(1-4x))/2. - T. D. Noe, Oct 08 2006
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MATHEMATICA
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nn=200; t=Rest[CoefficientList[Series[1-Sqrt[1-4x]/2, {x, 0, nn}], x]]; CoefficientList[Series[Product[(1+t[[k]]*x^k), {k, nn}], {x, 0, nn}], x] (* T. D. Noe, Oct 08 2006 *)
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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