🔢 Sum of Three Squares - 3D Crystal of Lattice Points on Spherical Shells: r3(n), Legendre's 4^a(8b+7) Gaps and Class Numbers

A Blender-built ball-and-stick integer lattice with glass spherical shells: pick n, see its r3(n) representations lit up with cubic symmetry, cumulative count versus volume, and live brute-force vs class-number checks.