new version added http://scratch.mit.edu/projects/Subh/1093746 I added a limit and a check to my last project. Upgraded, now it will use a limit (only when specified) and will automaticall stop before errors occur (in ONLINE mode) My original notes : This project is a very fast version of scmb1's project http://scratch.mit.edu/projects/scmb1/978284 and uses the formula of (2^n)-2/n. J is the no. to be checked and K is the value of (2^n)-2. Instead of generating k again and again, I used the previous values of k to generate the next value of k to speed it up. I guess it should be a lot faster. Feeling sorry for the maths involved Tell me if I'm wrong.