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Search: id:A005218
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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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+0
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; listen)
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OFFSET
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1,5
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REFERENCES
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N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
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.
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LINKS
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R. W. Robinson, Table of n, a(n) for n = 1..190
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FORMULA
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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
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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
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Sequence in context: A152982 A001642 A001643 this_sequence A131481 A001072 A077900
Adjacent sequences: A005215 A005216 A005217 this_sequence A005219 A005220 A005221
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KEYWORD
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nonn
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AUTHOR
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N. J. A. Sloane (njas(AT)research.att.com).
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EXTENSIONS
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More terms from Emeric Deutsch (deutsch(AT)duke.poly.edu), Nov 19 2004
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