NOTE: Scratch 3 now has a limit of 200000 list items, so this can now only list primes up to 2750159 :( ======================================= Here's an even faster version, using a sieve method :) It can find the 78498 primes up to a million in about 30 seconds (and in about 6 secs if you hide the list, but I thought it was quite nice to watch it grow...) The previous project (of which this is a remix) used an optimised trial division method to test if a number is prime. I said that a sieve-based method would be quicker in theory, but Scratch's list-replacing is slow when compared to just adding, and a sieve method needs to do lots of replacing - in fact, when I tried the most straightforward sieving, I found it was taking almost as long just to fill the whole list for sieving as the previous project took to find all the primes! However, I've come up with a way to do the sieve method which only sieves a chunk at a time. It sieves each chunk in turn, to find primes in there, before moving on to the next chunk. This turns out to make things *much* faster... :)
