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A003089
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Number of connected line graphs with n nodes.
(Formerly M1417)
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2
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1, 1, 2, 5, 12, 30, 79, 227, 710, 2322, 8071, 29503, 112822, 450141, 1867871, 8037472, 35787667, 164551477, 779945969, 3804967442, 19079312775, 98211456209, 518397621443, 2802993986619
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,3
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COMMENTS
| Sequence is identical to the number of connected graphs on n edges (A002905), except for the term a(3). The three connected 3-edge graphs (P_4, K_3 and K_{1,3}) yield only two linegraphs because K_3 and K_{1,3} have isomorphic linegraphs. No other connected nonisomorphic graphs have isomorphic linegraphs.
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REFERENCES
| F. Harary and E. M. Palmer, Graphical Enumeration, Academic Press, NY, 1973, p. 221.
R. C. Read and R. J. Wilson, An Atlas of Graphs, Oxford, 1998.
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
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LINKS
| Eric Weisstein's World of Mathematics. Line Graph.
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CROSSREFS
| Cf. A002905.
Sequence in context: A136704 A120895 A101785 * A179544 A112412 A193284
Adjacent sequences: A003086 A003087 A003088 * A003090 A003091 A003092
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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 R. C. Read (rcread(AT)math.uwaterloo.ca).
More terms from Gordon Royle (gordon(AT)maths.uwa.edu.au), Jun 05 2003
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