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A003244
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Number of unrooted achiral trees with n nodes.
(Formerly M0759)
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1
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1, 1, 1, 2, 3, 6, 9, 16, 23, 35, 51, 72, 97, 136, 186, 230, 321, 401, 526, 647, 844, 1000, 1331, 1539, 1960, 2299, 2943, 3307, 4237, 4779, 5961, 6744, 8372, 9239, 11605, 12694, 15549, 17264, 21086, 22784, 27976, 30357, 36598, 39843, 47821
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,4
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REFERENCES
| N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
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LINKS
| F. Harary and R. W. Robinson, The number of achiral trees, J. Reine Angew. Math., 278 (1975), 322-335.
Index entries for sequences related to trees
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FORMULA
| In terms of generating functions: A003244(x) = A003241(x)-(P^2(x)-P(x^2))/(2*x^2) with P(x)=x*A003238(x). [Harary & Robinson eq 45]. - R. J. Mathar, Sep 28 2011
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CROSSREFS
| Sequence in context: A006868 A067435 A035494 * A115995 A051057 A147364
Adjacent sequences: A003241 A003242 A003243 * A003245 A003246 A003247
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KEYWORD
| nonn,easy
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AUTHOR
| N. J. A. Sloane (njas(AT)research.att.com).
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EXTENSIONS
| Extended by R. J. Mathar, Sep 28 2011
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