has anyone got any good rules for remembering prime numbers?

Answer 1

There is no rule per se. But for an integer n, you only have to test for factors up to sqrt(n.) In particular, if you are thinking about numbers < 100, then you only need to test to see if the number is divisible by prime numbers < 10.

So, you check for 2, 3, 5, 7.

So for a number n, between 10 and 100, is it a prime? Well, if it is divisible by 2 or 5, you can tell right away. 3 is pretty simple too as if 3 divides n, the sum of the digits in n is divisible by 3. So you really only need to check 7.

Answer 2

the prime number is the number which has only two factors ( 1 and the number itself ) such as 2, 3 ,5 7,11 .....
notice that
1 is not a prime number because it has only one factor
2 is the only even prime number
All the other prime numbers are odd
Not all the odd numbers are prime

Answer 3

The only one I know is that an even number cannot be prime, except for 2.
.

Answer 4

The only one I remember is that:
A prime number is a number that can only be divided by itself and 1.
The first prime number is 2
The first few prime numbers are:-
2,3,5,7,11,13,17,19----------

Answer 5

Sorry ,there are not such rules