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A007139
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Number of unlabeled bicolored graphs on 2n nodes having n nodes of each color and allowing the color classes to be interchanged.
(Formerly M4172)
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5
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1, 2, 6, 26, 192, 3014, 127757, 16853750, 7343780765, 10733574184956, 52867617324773592, 882178116079222400788, 50227997322550920824045262, 9837048598740665027344331562224, 6681839615514161556535851222043192179
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,2
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REFERENCES
| F. Harary, L. March and R. W. Robinson, On enumerating certain design problems in terms of bicolored graphs with no isolates, Environment and Planning, B 5 (1978), 31-43.
R. W. Robinson, Numerical implementation of graph counting algorithms, AGRC Grant, Math. Dept., Univ. Newcastle, Australia, 1976.
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
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FORMULA
| a(n) = (A002724(n)+A122082(n))/2. - Vladeta Jovovic (vladeta(AT)eunet.rs), Feb 27 2007
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CROSSREFS
| Cf. A007140, A122081.
Sequence in context: A086584 A032014 A112948 * A162438 A137071 A034565
Adjacent sequences: A007136 A007137 A007138 * A007140 A007141 A007142
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KEYWORD
| nonn
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AUTHOR
| N. J. A. Sloane (njas(AT)research.att.com).
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EXTENSIONS
| More terms from Vladeta Jovovic (vladeta(AT)eunet.rs), Feb 27 2007
Edited by N. J. A. Sloane (njas(AT)research.att.com), Aug 14 2007
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