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Prime No.

Pawan Arora
Ranch Hand

Joined: Sep 14, 2008
Posts: 105
Hi, I want to find out 10001st prime number of the site Projecteuler, and here is my programme

and I'm getting the answer as 104149. I thougth I've written my code correctly, but yet I'm getting wrong answer. Could anyone please tell me the reason of not having a right result? A small hint is enougth.
Ulf Dittmer
Marshal

Joined: Mar 22, 2005
Posts: 42913
    
  68
What does isPrime(25) return?
Campbell Ritchie
Sheriff

Joined: Oct 13, 2005
Posts: 40034
    
  28
When you get prime(25) to return true, get a pencil and paper, and write 1 2 3 4 . . . 24 25. Then go through your method (a complicated bit of programming, there) and work out which numbers it will reject. You need to count the iterations of the loop carefully.

Then find out how the "Sieve of Eratosthenes" works. Far better way of working out prime numbers.
 
It is sorta covered in the JavaRanch Style Guide.
 
subject: Prime No.