what is the greatest prime you must consider to test wheather 5084 is prime??

the greatest prime to consider is....

Question

what is the greatest prime you must consider to test wheather 5084 is prime??

the greatest prime to consider is....

anonymous · Answer

whatever prime is just below 
$$\sqrt{5084}$$

anonymous · Answer

i dont get how to solve that though

anonymous · Answer

a calculator gives me 71. something, so i would say up until 71

anonymous · Answer

thank you.. how do i find squar root?

anonymous · Answer

which is a prime for sure

anonymous · Answer

how do i do it on a calculator

anonymous · Answer

actually  it is fairly clear that 5084 is divisible by 4. if you divide you get 1271 so i guess i was  wrong. you only need to check up to what ever is just below 
$$\sqrt{1271}$$

anonymous · Answer

71 was the right answer though

anonymous · Answer

well if it is on line i guess you can say that.  fine

anonymous · Answer

It seems like, you have to test up to sqrt(n) where n is the number you are testing. So, sqrt(5084) is right.

anonymous · Answer

You really don't need a calculator in this case. You can tell that 70*70 = 4900. So, it is higher than 70. Then do 71*71 and see how close it gets to 5084. That should be your answer. Of course, calculators are easy to use.

anonymous · Answer

well only it it is not entirely obvious from your eyeballs that 5084 is divisible by 4.

anonymous · Answer

The fact that it is divisible by 2 makes it a not-prime number. It does not matter that it is divisible by 4. The largest number you can possibly test is sqrt(n). So, 71 in this case.