http://projecteuler.net/problem=35 - The number, 197, is called a circular prime because all rotations of the digits: 197, 971, and 719, are themselves prime.  There are thirteen such primes below 100: 2, 3, 5, 7, 11, 13, 17, 31, 37, 71, 73, 79, and 97.  How many circular primes are there below one million?