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Search: id:A058737
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| 1, 1, 3, 7, 20, 55, 162, 477, 1450, 4446, 13858, 43589, 138515, 443487, 1430261, 4640312, 15137893, 49620637, 163360133, 539904503, 1790699059, 5958280016, 19883532941, 66532519727, 223177199775, 750340752081, 2528058240115
(list; graph; listen)
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OFFSET
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2,3
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COMMENT
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Also the number of unlabeled cographs on n nodes with two components. - Vladeta Jovovic (vladeta(AT)Eunet.yu), May 07 2005
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REFERENCES
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J. Riordan, The blossoming of Schroeder's fourth problem, Acta Math., 137 (1976), 1-16.
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LINKS
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Eric Weisstein's World of Mathematics, Cograph
Index entries for sequences related to rooted trees
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FORMULA
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G.f.: A(x) = (B(x)^2+B(x^2))/2, where B(x) = g.f. for A000669. - Vladeta Jovovic (vladeta(AT)Eunet.yu), May 07 2005
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CROSSREFS
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Cf. A106240.
Sequence in context: A109220 A018034 A000227 this_sequence A129429 A084204 A132364
Adjacent sequences: A058734 A058735 A058736 this_sequence A058738 A058739 A058740
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KEYWORD
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nonn
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AUTHOR
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njas, Jan 01 2001
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EXTENSIONS
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More terms from Vladeta Jovovic (vladeta(AT)Eunet.yu), May 07 2005
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