prime number!!!?

Question

Is there any simple trick to know whether the given number is prime or not?

Answer 1

any eveen number is not prime

Answer 2

Unfortunately, I don't believe there is. However, you only need to divide the number by half the numbers you normally would. 17 isn't going to divide evenly into 20. You can stop at 10, because 2*10 = 20, and 2 is the next highest root from 1.

For example:

I have the number 23. I know it is divisible by itself and 1, so I write down 1 and 23. If I find any other numbers it is divisible by, I write them down too. Now, I try 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, and that's all I need to try. Any number that is more than half the original number can't be evenly divisible. Because none of the other numbers I tried worked, I conclude that 23 is a prime number.

Answer 3

All I know is that if the # is even then it is not a prime number... it's divisible by 2. If the number is kind of big, then you can make it easier to tell if it's divisible by 3 by adding all the digits together. Example: 519... 5+1+9=15 and 15 is divisible by 3. (519 is not prime) Uh... prime numbers are a pain in the butt, you just have to go through the numbers and see if they will go into the number in question evenly, or find a chart or something. Sorry, I know that's not very clear but maybe it will help?

Answer 4

Well, if it's even number greater than 2, it's not prime. (2 itself, however, is prime.) Also, if you add up the digits of the number and the sum is divisible by 3--it's not prime. (for example...take 129. The sum of the digits is 1+2+9, which equals 12. 12 is divisible by 3. Therefore 129 is not prime.)

Or if it ends in a 5 and is greater than 5, it's not prime.

Those are about the easiest

Answer 5

If you figure out the square root of the highest number in your possible set of numbers, or the square root of the next highest number after your set. This will give you an upper range for the numbers you need to test.

So lets say you want to find all the prime numbers from 1 to 110. The square root of 110 is not a whole number so use 11 (square root of 121).

Make a list of all the numbers from 1 to 110. Circle 1, 2, and 3 because they are all prime.
Now Cross off any number that can be divided by 2. This will get rid of half the numbers in your set. Next, cross off all the numbers divisible by 3. 4 and all its multiples will already be crossed of as it is divisible by 2.

Circle 5 since it is not crossed off and there are no numbers left to divide it by. Cross out all the numbers divisible by 5.

6 will already be gone as will all its multiples because they will also have been shared by 2 or3.

Circle 7 Since there is nothing left to divide it by. Cross out all the numbers divisible by 7.

8 will be gone as will 9 and 10 as will all their multiples since they will have been part of previously eliminated sets.

Now cross out all the multiples of 11 and circle 11 because there are no numbers left to divide it by.

The numbers you have left will be the prime numbers.

Circle 11.

Answer 6

a prime number is a number that is divisible by its self, like 1 3 5 7 11 13 17

Answer 7

If the number is divisible by itself & the number 1 only, then it is safe to say that it is a prime number.

Answer 8

Divide tthe # by 2 and if its not a fractional number then you know its a prime #. In short it should not have have more than 2 facts i.e the #1 and the number itself.

Answer 9

First it has to be odd.
Then divide the number in question, say n by 3 through sqrt(n) iteratively skipping powers of 2.

ie n/3 then n/5 then n/6 then n/7 then n/9...

if there are remainders at each step, then its prime. There are some short cuts, but what do you want for free...

Answer 10

A prime number is a number that can only be divided by itself and by 1 without having a remainder.

Answer 11

A prime number is a whole number greater than 1 that can only be divided evenly by itself and 1....