## Euler 035 - counting circular primes

How many circular primes (primes that when rotated are still primes) are there below one million?

See Problem 20.

Again, this rescues a lot of code from previous problems, but the solution is less than perfect. The Euler guidelines say that every problem should be computable within a minute, but despite much tweaking, this solution takes significantly longer.

For speed, primes should be generated only once …