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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;
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refs;
listen;
history;
text;
internal format)
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OFFSET
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1,5
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REFERENCES
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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
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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, 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); # Emeric Deutsch, Nov 19 2004
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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