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A000684
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Number of colored labeled n-node graphs with 2 interchangeable colors.
(Formerly M2954 N1192)
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3
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1, 3, 13, 81, 721, 9153, 165313, 4244481, 154732801, 8005686273, 587435092993, 61116916981761, 9011561121239041, 1882834327457349633, 557257804202631217153, 233610656002563147038721, 138681207656726645785559041
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,2
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REFERENCES
| F. Harary and R. W. Robinson, Labeled bipartite blocks, Canad. J. Math., 31 (1979), 60-68.
D. A. Klarner, The number of graded partially ordered sets, J. Combin. Theory, 6 (1969), 12-19.
A. Nymeyer and R. W. Robinson, ``Tabulation of the Numbers of Labeled Bipartite Blocks and Related Classes of Bicolored Graphs,'' unpublished manuscript, 1982.
R. W. Robinson, Numerical implementation of graph counting algorithms, AGRC Grant, Math. Dept., Univ. Newcastle, Australia, 1976.
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
| R. W. Robinson, Table of n, a(n) for n = 1..32
S. R. Finch, Bipartite, k-colorable and k-colored graphs (2*A000684)
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FORMULA
| G.f.: A(x) = Sum_{n>=1} x^n/(1 - 2^n*x)^n. [From Paul D. Hanna (pauldhanna(AT)juno.com), Sep 14 2009]
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MATHEMATICA
| With[{nn=20}, Rest[CoefficientList[Series[Sum[x^n/(1-2^n x)^n, {n, nn}], {x, 0, nn}], x]]] (* From Harvey P. Dale, Nov 24 2011 *)
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PROG
| (PARI) a(n)=polcoeff(sum(k=1, n, x^k/(1-2^k*x +x*O(x^n))^k), n) [From Paul D. Hanna (pauldhanna(AT)juno.com), Sep 14 2009]
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CROSSREFS
| 2 * A000683(n) + 1. Cf. A058872.
Sequence in context: A135921 A005923 A089461 * A057993 A000904 A201304
Adjacent sequences: A000681 A000682 A000683 * A000685 A000686 A000687
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KEYWORD
| nonn,nice,easy
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AUTHOR
| N. J. A. Sloane (njas(AT)research.att.com).
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EXTENSIONS
| a(15) onwards added by N. J. A. Sloane (njas(AT)research.att.com), Oct 19 2006 from the Robinson reference
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