Fun with prime numbers
I find the study of prime numbers to be one of the most fulfilling worldly pursuits, and the fine folks at NumberSpiral.com demonstrate some truly fascinating patterns in the primes and endeavor to explain them using interesting and not-too-complicated math.

The site utilizes an extremely helpful, visual method to demonstrate the patterns. It even offers the website of the graphical program they used to generate the spiral, complete with instructions as to how to recreate all results. How handy!
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