Well, I haven't made a project in a while, started feeling guilty about that, so here's a little tool that I made in under an hour. It just calculates prime numbers, nothing fancy or exciting really (unless you like prime numbers a lot?). Probably should run in turbo if you're using a big range (shift-click the green flag in the Flash Viewer or in Scratch go to Edit > Set Single Stepping > Turbo Speed), otherwise it will take a long time. It's not really the most efficient script, but it gets the job done (...eventually!)
