When choosing the exclusion shells, you only require those that are wholly divisible into 30. Numbers less than the prime being plotted (3 & 2 in this case) don’t need to be included either. So for the 5 shell, the exclusion shells that make the reveal shell work are the 1, 5, 6, 10 & 15 shells.

The 7 shell

  1. The Reveal shell is 7× 5×3×2×1=210.
  2. The next prime number is 7...
  3. So the system works to 11^2=121.