OFFSET
0,4
LINKS
J. H. Conway and N. J. A. Sloane, Low-Dimensional Lattices II: Subgroups of GL(n,Z), Proc. Royal Soc. London, A 419 (1988), 29-68.
Gheorghe Coserea, Gram matrix.
G. Nebe and N. J. A. Sloane, Home page for this lattice
W. Plesken, Finite Unimodular Groups of Prime Degree and Circulants, J. Algebra, vol. 97 (1985), pp. 286-312.
PROG
(PARI) \\ system("wget https://oeis.org/A015163/a015163.txt");
g = matconcat(read("a015163.txt")~);
seq(N, g, flag=0) = concat(1, 2*Vec(qfrep(g, N, flag)));
seq(15, g) \\ Gheorghe Coserea, Nov 28 2018
(PARI)
GramMatrix()={my(p=[3, -1, 0, 0, 1, -1, 0, 1, 0, 0, 1, 0, -1, 1, 0, 0, -1]); matrix(#p, #p, i, j, p[(i-j) %#p + 1])}
a(n)={if(n==0, 1, 2*qfrep(GramMatrix(), n, 0)[n])} \\ Andrew Howroyd, Nov 29 2018
CROSSREFS
KEYWORD
nonn
AUTHOR
EXTENSIONS
More terms from Gheorghe Coserea, Nov 28 2018
STATUS
approved