0,2

N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

J. H. Conway and N. J. A. Sloane, "Sphere Packings, Lattices and Groups", Springer-Verlag, p. 125. Equation (112)

G. Nebe and N. J. A. Sloane, Home page for this lattice

Expansion of phi(q)^3*(phi(q)^4 +7*16*q*psi(q^2)^4) in powers of q where phi(),psi() are Ramanujan theta functions. - Michael Somos Oct 24 2006

1 + 126*q^2 + 756*q^4 + 2072*q^6 + 4158*q^8 + 7560*q^10 + 11592*q^12 + ...

(PARI) {a(n)=local(A); if(n<0, 0, A=sum(k=1, sqrtint(n), 2*x^k^2, 1+x*O(x^n)); polcoeff( 8*A^7 -7*A^3*subst(A, x, -x)^4, n))} /* Michael Somos Oct 24 2006 */

(PARI) {a(n)= if(n<1, n==0, 2*qfrep([2, -1, 0, 0, 0, 0, 0; -1, 2, -1, 0, 0, 0, 0; 0, -1, 2, -1, 0, 0, 0; 0, 0, -1, 2, -1, 0, -1; 0, 0, 0, -1, 2, -1, 0; 0, 0, 0, 0, -1, 2, 0; 0, 0, 0, -1, 0, 0, 2], n, 1)[n])} /* Michael Somos Jun 11 2007 */

Sequence in context: A154039 A165023 A107658 this_sequence A126170 A151989 A104678

Adjacent sequences: A004005 A004006 A004007 this_sequence A004009 A004010 A004011

nonn,easy

N. J. A. Sloane (njas(AT)research.att.com).