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Search: id:A002861
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| A002861 |
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Number of connected functions (or mapping patterns) on n unlabeled points, or number of rings and branches with n edges.
(Formerly M1182 N0455)
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+0
13
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| 1, 2, 4, 9, 20, 51, 125, 329, 862, 2311, 6217, 16949, 46350, 127714, 353272, 981753, 2737539, 7659789, 21492286, 60466130, 170510030, 481867683, 1364424829, 3870373826, 10996890237, 31293083540
(list; graph; listen)
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OFFSET
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1,2
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REFERENCES
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S. R. Finch, Mathematical Constants, Cambridge, 2003, Section 5.6.6.
R. A. Fisher, Contributions to Mathematical Statistics, Wiley, 1950, 41.399.
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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C. G. Bower, Table of n, a(n) for n = 1..500
C. G. Bower, Transforms (2)
INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 118
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FORMULA
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CIK transform of A000081.
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MAPLE
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spec2861 := [B, {A=Prod(Z, Set(A)), B=Cycle(A)}, unlabeled]; [seq(combstruct[count](spec2861, size=n), n=1..27)];
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CROSSREFS
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Cf. A000081, A001372.
Sequence in context: A128496 A134955 A027881 this_sequence A032200 A130969 A034750
Adjacent sequences: A002858 A002859 A002860 this_sequence A002862 A002863 A002864
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KEYWORD
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nonn,nice
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AUTHOR
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N. J. A. Sloane (njas(AT)research.att.com).
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EXTENSIONS
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More terms from Philippe Flajolet and Paul Zimmermann, Mar 15 1996.
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