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A005218
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Number of unlabeled reduced unit interval graphs on n nodes.
(Formerly M2369)
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1
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0, 0, 1, 1, 3, 4, 11, 21, 55, 124, 327, 815, 2177, 5712, 15465, 41727, 114291, 313504, 866963, 2404251, 6701321, 18733340, 52557441, 147849031, 417080105, 1179355476, 3342487033, 9492629497, 27011665839, 77000574224
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,5
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REFERENCES
| Hanlon, Phil; Counting interval graphs. Trans. Amer. Math. Soc. 272 (1982), no. 2, 383-426.
R. W. Robinson, personal communication.
R. W. Robinson, Numerical implementation of graph counting algorithms, AGRC Grant, Math. Dept., Univ. Newcastle, Australia, 1980.
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..190
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FORMULA
| G.f.=-z+(1/4)(1+2z-z^2)/sqrt[(1+z^2)(1-3z^2)]-(1/4)sqrt[(1-3z)/(1+z)] - Emeric Deutsch (deutsch(AT)duke.poly.edu), Nov 19 2004
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MAPLE
| G:=-z+(1+2*z-z^2)/4/sqrt((1+z^2)*(1-3*z^2))-sqrt((1-3*z)/(1+z))/4: Gser:=series(G, z=0, 30): seq(coeff(Gser, z^n), n=1..28); (Deutsch)
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CROSSREFS
| Sequence in context: A152982 A001642 A001643 * A131481 A001072 A077900
Adjacent sequences: A005215 A005216 A005217 * A005219 A005220 A005221
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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 Emeric Deutsch (deutsch(AT)duke.poly.edu), Nov 19 2004
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