OFFSET
1,2
COMMENTS
lim n->infinity a(n)/n^3 = Pi/6.
EXAMPLE
a(2)=4 because the 4 lattice points in the first octant (x,y,z)={(1,1,1), (1,1,3), (1,3,1), (3,1,1)} all satisfy x^2+y^2+z^2 < (2*2)^2.
CROSSREFS
KEYWORD
nonn
AUTHOR
Hugo Pfoertner, Jul 12 2006
STATUS
approved