Starting from the center of the picture, the spheres are
numbered (N=1, 2, 3,..., 1024) when following a
square spiral. The radius of the N-th sphere is proportional
to the square root of the number of divisors of N.
The number 1 and the prime numbers are visualized by means of white spheres
(a smaller one for the number 1).
Other numbers are visualized by means of colored spheres
(the luminance varies according to the number of divisors).
