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# Is 599 and 807 a prime number?

How do you test to see if 599 is a prime or 807 is a prime number?

Thank you

It's easier to see if a number is not prime than it is to see if a number is prime. For example, 807 is not prime, because it's divisible by 3 (its digits add to a multiple of 3).

As for 599, you would have to check by some method, probably the most straightforward being trial division. That is, you would test divisibility each number less than 599. You can make it a bit more efficient by only testing primes less than the square root of 599 (which is approximately 24.47, so you'd only test up to 24. The primes less than 24 are:

2, 3, 5, 7, 11, 13, 17, 19, 23

We can easily eliminate 2, 3, and 5. The others you can test if you know the tests, but it's probably just as easy to divide by each of them. If you do, you'll see that none of them divide 599 evenly, so 599 is prime.

599 is

807 is not (divisible by 3)

I used trial and error, but I'm sure there are easier ways (been awhile since I've taken math). The easiest way to determine if something is divisible by 3 is add up each digit and see if the sum is a number that you KNOW is divisible by 3. 8+0+7=15.

add the numbers together - LOL

5 + 9 + 9 = 23

2 + 3 = 5 can't divide by three

not even - can't divide by 2

not a 5 or 0

807 = 8 + 0 + 7 =15

1 + 5 = 6 6 you can divide by 3

807 /3 = 269

all the best