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A018843 Number of n-dimensional unimodular lattices without roots. 0
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; text; internal format)
OFFSET

0,25

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.

LINKS

Table of n, a(n) for n=0..28.

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

CROSSREFS

Sequence in context: A271699 A216701 A278326 * A152836 A152837 A182036

Adjacent sequences:  A018840 A018841 A018842 * A018844 A018845 A018846

KEYWORD

nonn,hard

AUTHOR

N. J. A. Sloane, Roland Bacher

EXTENSIONS

The paper by Oliver King (king(AT)math.berkeley.edu) shows that a(29) >= 8900 and a(30) >= 82000000.

STATUS

approved

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Last modified November 12 19:33 EST 2019. Contains 329078 sequences. (Running on oeis4.)