Instructions:

Try to find a generator for a group. Select a number n from the drop box on the left. Select a number m from the horizontal list of numbers, all of which are prime relative to n. Click the Multiply button and watch boxes turn yellow. Each is mk mod n for some k (given by the count textfield). A generator has been found if many clicks on Multiply turn all gray boxes to yellow. Use the reset button to try another generator.

Observe:

If n is prime there is a number in Z*n, called a generator and denoted g, such that gi, 1≤i<n, is unique, and an element of Z*n and gn-1 is 1. A generator for n = 19 is 10.