Click a green flag. I recommend turbo mode (shift+click green flag). All primes up to answer are computed using the sieve of Eratosthenes. If your answer is empty 12000 is used. A note corresponding to the marked number is played. The stopwatch stops when the sieve is done, but after that the non-primes are deleted from the list, which can take a long time. You can toggle hide or show the list by clicking on the stage, and when hidden the computations are much faster. SPACE restarts.
https://en.wikipedia.org/wiki/Sieve_of_Eratosthenes I used Tosh as editor: https://scratch.mit.edu/discuss/topic/192915/?page=1 It also works in Phosphorus, except no visible list: http://phosphorus.github.io/#135346157 http://phosphorus.github.io/app.html?id=135346157&turbo=true&full-screen=true On my Lenovo Ideapad 100 computer 12000 numbers takes 150.2 s in turbo mode on Scratch, and 111.6 s in turbo mode on Phosphorus. On my Raspberry Pi 2 computer 12000 numbers takes 591.9 s in turbo mode on Scratch, and 153.0 s in turbo mode on Phosphorus.
