Well while I enjoyed my fathers day sleep-in this morning, I worked through why the example Sieve of Eratosthenes works. When for example the outer loop is at 4, you can start at 16 (4*4) due to the 2, 3 times of 4 been taken care of when the outer loop was 2 and 3. So now I’m feeling a bit silly for not seeing it at the time. But at least I can now use it, with confidence.
I also walked through how to solve the first part of the 550 point problem. Now I going to sit down and work through the string building part.