OFFSET
1,3
COMMENTS
a(4) and a(5) are determined by Odlyzko and Sloane, a(6) by Peters and Kok Seng Chua gives an explicit upper bound for all a(n). Also both a(7) and a(8) are either 2 or 3 as established by Chakraborty et al.
LINKS
K. Chakraborty, A. K. Lal and B. Ramakrishnan, Modular forms that behave like theta series, Math. Computation, Vol. 66, 219, Jul 15 1997, pp. 1169-1183
Kok Seng Chua, An explicit Hecke's bound and exceptions of even unimodular quadratic forms, Bull. Austral. Math. Soc. 65 (2002), 231-238.
A. M. Odlyzko and N. J. A. Sloane, On exceptions of integral quadratic forms, J. reine angew Math. 321, 212-216, (1981)
M. Peters, Definite Unimodular 48-Dimensional Quadratic Forms, Bull. London Math. Soc., 15 (1983), 18-20
EXAMPLE
a(3)=2 because Leech lattice has no vectors of norm 2. All other 24-dimensional Niemeier lattices contains vectors of all even norms.
CROSSREFS
KEYWORD
nonn,hard,more
AUTHOR
Kok Seng Chua (chuaks(AT)ihpc.nus.edu.sg), May 25 2000
STATUS
approved