Template:Task

You are encouraged to solve this task according to the task description, using any language you may know.

A twin prime is a pair of natural numbers P1 and P2 that satisfy the following:

1. P1 and P2 are primes

2. P1 + 2 = P2

Write a program that displays the number of twin primes that can be found under a user-inputted number.

Examples below:

Output:

> Search Size: 100
> 8 twin prime pairs.

> Search Size: 1000
> 35 twin prime pairs.

Java

BigInteger implementation: <lang Java> import java.math.BigInteger; import java.util.Scanner;

public class twinPrimes {

   public static void main(String[] args) {
       Scanner input = new Scanner(System.in);
       System.out.println("Search Size: ");
       BigInteger max = input.nextBigInteger();
       int counter = 0;
       for(BigInteger x = new BigInteger("3"); x.compareTo(max) <= 0; x = x.add(BigInteger.ONE)){
           BigInteger sqrtNum = x.sqrt().add(BigInteger.ONE);
           if(x.add(BigInteger.TWO).compareTo(max) <= 0) {
               counter += findPrime(x.add(BigInteger.TWO), x.add(BigInteger.TWO).sqrt().add(BigInteger.ONE)) && findPrime(x, sqrtNum) ? 1 : 0;
           }
       }
       System.out.println(counter + " twin prime pairs.");
   }
   public static boolean findPrime(BigInteger x, BigInteger sqrtNum){
       for(BigInteger divisor = BigInteger.TWO; divisor.compareTo(sqrtNum) <= 0; divisor = divisor.add(BigInteger.ONE)){
           if(x.remainder(divisor).compareTo(BigInteger.ZERO) == 0){
               return false;
           }
       }
       return true;
   }

} </lang>

Output:

<pre>
> Search Size:
> 100
> 8 twin prime pairs.

> Search Size:
> 1000
> 35 twin prime pairs.