2: 0.505605644621
    3: 0.655044609005
    4: 0.698131700798
    7: 0.795664955850
   19: 0.829031394697

2 3 4 7 19

Fit of radii by a power law r = a0*n^a1:
  a0 = 0.74861  a1 = -0.45811