The K-smooth integers on a generalized Ulam spiral [Les entiers K-friables sur une spirale d'Ulam généralisée].
Starting from the center of the picture, the spheres are
numbered (N=2,..., 16130) when following a
square spiral. The radius of the sphere displaying the number N is an decreasing function
of the logarithm of the smoothness K of N (K being the largest prime factors of N).
Nota: the logarithm of K (inside [2,9.688] and renormalized inside [2,255])
is displayed using the following palette. Then the luminance is too a decreasing function of the logarithm of K.
