Ok. Im terrible at writing so hope this make sense. I've noticed that all prime numbers are a multiple of 2520, plus a prime less than 2520 (1 is the exception and must be included) will always be prime. For example 2539 is 2520 plus 19. 5059, 10099, 12619, 15139 are all prime and all multiples of 2520 plus 19. So from this I have done an addition grid with all primes up too 2520 (including 1) along the top, and all multiples of 2520 running down, now not all numbers on this grid are prime but it does show all possible primes. So from this I have concluded that to find out if a number ending in 1,3,7,9 is not prime all you have to do is find the closest lower number dividable by 2520, subtract that from your original number and if the result isn't a prime number less than 2520 than that number cannot be prime. Am I missing something here? I've tried it with a few numbers up too 9 digits and it works every time. And seeing as all primes are linked to 2520 and the addition of a prime less than 2520 would this not mean their is a pattern to prime numbers?