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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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14
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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; refs; listen; history; internal format)
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OFFSET
| 1,2
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REFERENCES
| 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
| 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
| CIK transform of A000081.
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MAPLE
| 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
| Cf. A000081, A001372.
Sequence in context: A134955 A171887 A027881 * A032200 A130969 A034750
Adjacent sequences: A002858 A002859 A002860 * A002862 A002863 A002864
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KEYWORD
| nonn,nice
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AUTHOR
| N. J. A. Sloane (njas(AT)research.att.com).
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EXTENSIONS
| More terms from Philippe Flajolet and Paul Zimmermann, Mar 15 1996.
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