I 'm confused about prime number.
It is possible that we can find a not prime number that is greater than 100 and not divided by {2,3,5,7,9}.
because someone said to me that we can check if a number(greater than 100) is prime just to check if it is not divided by {2,3,5,7,9}
Thank you
Best Answer
One can check that a number smaller than 100 is a prime just by checking that it is not divisible by 2, 3, 5, 7.
This is because the next prime after 7 is 11, whose square is greater than 100 (hence the test holds if one replaces 100 by 120, note also that checking the divisibility by 9 is useless since 3 divides 9).