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,..., 261122) when following a
square spiral. The radius of the sphere displaying the number N is an increasing function
of the smoothness K of N (K being the largest prime factors of N).
Nota: K (inside [2,261101] and renormalized inside [2,255])
is displayed using the following palette. Then the luminance is a decreasing function of K.
