How do you learn the prime numbers?

Answer 1

It's mostly abut knowing what isn't a Prime number and for that you need to know your multiplication tables and your divisibility rules. The only even prime number is 2. Every other even number is not prime. Any number whose digits add up to a multiple of three is a multiple of three. Not prime. The only prime number that ends in 5 is 5. All others, not prime. You know that 63 is not prime because 7 x 9 = 63. You know that 47 is prime because nothing goes into it except one and itself. You can memorize the first ten or so. 2, 3, 5, 7, 11, 13, 17, 19, 23, 29. All multiples of those numbers are not prime. That should get you started.

Answer 2

For numbers below 121, use the following rules:

1. 2, 3, 5 and 7 are prime.
2. Otherwise, numbers ending in 0,2,4,5,6, or 8 are composite
3. Add the digits in the number. If the answer has more than one digit, add those. If the result is 3,6 or 9, the number is composite.
4. 49, 77 and 91 are composite.
5. Everything else is prime.

Now, everybody sit in a circle, and stomp and clap to "We Will Rock You". Each time you clap, say the next number. But don't say the primes!!

Stomp, stomp, clap!

Stomp, stomp, clap!

Stomp, stomp, FOUR!

Stomp, stomp, clap!

Stomp, stomp, SIX!

Stomp, stomp, clap!

Stomp, stomp, EIGHT!

Stomp, stomp, NINE!

Stomp, stomp, TEN!

Stomp, stomp, clap!

Stomp, stomp, TWELVE!

and so on.

Anybody screws up, they do 5 pushups, and the game starts over.