The latest activity on Visnos, a reimagined version of the Sieve of Erastosphenes. Although there are other versions of the sieve on web, most are just a rehash of the standard method used by school students across the globe.
This version has a small but crucial difference, it allows more than one color per square. This in fact opens up lots of extra ways to use the grid. By using a different color to represent each prime number, eliminated numbers can reveal their prime factors.
Additionally the group can be used for finding the Lowest Common Multiple of a set of numbers. The example shown on the right, shows finding the LCM of 4,5 and 10. Each multiple is given a different color, red is 4, lime is 5 and yellow is 10. You can see all the multiples for each number, but also each color is present on 20 which means it is the LCM.
When using the square as a sieve, the colors give the prime factors of each number. More information of how to use the activity can be found by clicking the info icon once launched.