3 is prime                0.01sec
4 is not prime            0.00sec
11 is prime               0.00sec
15 is not prime           0.00sec
1257787 is prime          0.17sec
1257788 is not prime      0.16sec
10000987 is prime         1.27sec
10000988 is not prime     1.26sec
123456791 is prime        15.93sec
123456792 is not prime    15.80sec
2147483647 ???            >3mins
2147483646 ???            >3mins