Goldbach's conjecture - http://en.wikipedia.org/wiki/Goldbach%27s_conjecture

goldbach.java

package com.testes;

/* Demonstrates the Goldbach's conjecture - Every even integer greater than 2 can be expressed as the sum of two primes
*
* author: Luiz Vessosa 
*/
 

import java.util.ArrayList;

import java.util.List;

 

public class Euler {

 

   private static final int NUM_TO_TEST = 134;

 

   public static void main(String[] args) {

      List<Integer> primes = primeGen(NUM_TO_TEST);

      System.out.println("Current Number: " + NUM_TO_TEST);

      System.out.print(NUM_TO_TEST + " = ");

 

      boolean foundSomething = false;

 

      for (int i = 0; i < primes.size(); i++) {

         for (int j = i; j < primes.size(); j++) {

            if ((primes.get(i) + primes.get(j)) == NUM_TO_TEST) {

               if (foundSomething)

                  System.out.print(" or ");

 

               System.out.print(primes.get(i) + " + " + primes.get(j));

 

               foundSomething = true;

            }

         }

      }

 

   }

 

   private static List<Integer> primeGen(int max) {

      int x, y = 0;

      List<Integer> result = new ArrayList<Integer>();

      for (x = 2; x < max; x++) {

         if (x % 2 != 0 || x == 2) {

            for (y = 2; y <= x / 2; y++) {

               if (x % y == 0) {

                  break;

               }

            }

            if (y > x / 2) {

               result.add(x);

               //System.out.println(x);

            }

         }

      }

      return result;

   }

 

}