[math-fun] Mental factoring

Take a number like 2257 (say < 10000), easily checked to have no prime factors < 13. To find the least prime factor of such a number N, is there on average a faster way (after having excluded primes < 13) than the naïve method of dividing it by each prime in order <= sqrt(N) until one divides N evenly? --Dan ________________________________________________________________________________________ It goes without saying that .