login
The OEIS is supported by the many generous donors to the OEIS Foundation.

 

Logo
Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A002844 Number of non-isentropic binary rooted trees with n nodes.
(Formerly M1445 N0571)
2
1, 1, 2, 5, 13, 36, 102, 296, 871, 2599, 7830, 23799, 72855, 224455, 695303, 2164491 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,3
COMMENTS
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."
REFERENCES
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).
LINKS
Tyler Foster, A Noncommutative Version of the Natural Numbers, arXiv:1003.2081 [math.QA], 2010. See D(n) Table 2 p. 3.
R. K. Guy, Letter to N. J. A. Sloane, June 24 1971: front, back [Annotated scanned copy, with permission] See sequence C.
Doron Zeilberger, Maple program for A002844
CROSSREFS
Bears a superficial resemblance to A036765.
Sequence in context: A346738 A116409 A279196 * A223096 A277996 A370168
KEYWORD
nonn,more
AUTHOR
EXTENSIONS
Revised by N. J. A. Sloane, Dec 15 2016
a(11)-a(14) from Doron Zeilberger, Jan 31 2017
a(15)-a(16) from Sean A. Irvine, Sep 29 2023
STATUS
approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified March 28 05:39 EDT 2024. Contains 371235 sequences. (Running on oeis4.)