Distribution of Primes

This is a chart of how the primes are distributed. By arranging the numbers in a square, we get to see them in terms of modular arithmetic (in a way, that's using multiples). For example in the 5x5, the 2nd column represents 2, 2+5, 2+10, 2+15, and 2+20. What patterns do you notice? Where do primes happen? Karl Gauss noticed that the farther up you go, the less primes there are. Can you see that here or do we need bigger numbers still?
More GeoGebra at mathhombre.blogspot.com/p/geogebra.html The idea for how to do this with the lists came from the forum: http://www.geogebra.org/forum/viewtopic.php?f=2&t=27574&p=95396 It's a post by the amazing Anthony Or. http://www.geogebratube.org/user/profile/id/191