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A002844
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Number of non-isentropic binary rooted trees with n nodes.
(Formerly M1445 N0571)
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2
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1, 1, 2, 5, 13, 36, 102, 296, 871, 2599, 7830, 23799, 72855, 224455, 695303, 2164491
(list;
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refs;
listen;
history;
text;
internal format)
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OFFSET
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1,3
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COMMENTS
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From Richard Guy's 1971 letter: "[Studied by] Helen Alderson, J. H. Conway, etc. at Cambridge. These are rooted trees with two branches at each stage and if A,B,C,D (see drawing [in letter]) are further growths, then one treats (AB)(CD) as equivalent to (AC)(BD) - otherwise one distinguishes left and right. [The sequence gives] the number of equivalence classes of such trees."
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REFERENCES
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R. K. Guy, personal communication.
N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
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LINKS
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R. K. Guy, Letter to N. J. A. Sloane, June 24 1971: front, back [Annotated scanned copy, with permission] See sequence C.
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CROSSREFS
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Bears a superficial resemblance to A036765.
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KEYWORD
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nonn,more
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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