# which numbers are prime

• Mar 9th 2008, 04:50 PM
rcmango
which numbers are prime
which numbers are prime?

a. 667

b. 557

i tried using numbers like (23)^2

and (24)^2

I didn't know how to prove this. Please show what needs to be done.
• Mar 9th 2008, 05:24 PM
topsquark
Quote:

Originally Posted by rcmango
which numbers are prime?

a. 667

b. 557

i tried using numbers like (23)^2

and (24)^2

I didn't know how to prove this. Please show what needs to be done.

Try factoring them.

For example, divide 667 by 2. It gives a decimal. So try 667/3, 667/5, 667/7 until you get to about $\sqrt{667}$. If you have no factors yet, then the number is prime.

I get that 557 is prime and 667 is composite.

-Dan
• Mar 9th 2008, 07:51 PM
rcmango
okay, 667 = 23 * 29

thankyou for the help.