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A018843
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Number of n-dimensional unimodular lattices without roots.
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0
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1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 2, 0, 1, 3, 38
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,25
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REFERENCES
| R. Bacher and B. B. Venkov, Reseaux entiers unimodulaires sans racine en dimension 27 et 28, in Reseaux euclidiens, designs spheriques et formes modulaires, pp. 212-267, Enseignement Math., Geneva, 2001.
J. H. Conway and N. J. A. Sloane, "Sphere Packings, Lattices and Groups", Springer-Verlag, p. 416, 424.
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LINKS
| R. Bacher and B. B. Venkov, Reseaux entiers unimodulaires sans racine en dimension 27 et 28 (html, ps).
O. King, A mass formula for unimodular lattices with no roots
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CROSSREFS
| Sequence in context: A195772 A062104 A153506 * A152836 A152837 A174996
Adjacent sequences: A018840 A018841 A018842 * A018844 A018845 A018846
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KEYWORD
| nonn,hard
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AUTHOR
| N. J. A. Sloane (njas(AT)research.att.com), Roland Bacher (Roland.Bacher(AT)ujf-grenoble.fr)
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EXTENSIONS
| The paper by Oliver King (king(AT)math.berkeley.edu) shows that a(29) >= 8900 and a(30) >= 82000000.
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