## java videos

### This program was asked in ISC 2018 Practical computer science paper. It a called Gold Bach number.

A Gold Bach number is a positive even integer that can be expressed as the sum of two odd primes.

Note: All even integer numbers greater than 4 are Gold Bach numbers.

Example:

6 = 3 + 3

10 = 3 + 7

10 = 5 + 5

Hence, 6 has one odd prime pair 3 and 3. Similarly, 10 has two odd prime pairs, i.e. 3, 7 and 5, 5.

Write a program to accept an even integer â€˜Nâ€™ where N > 9 and N < 50. Find all the odd prime pairs whose sum is equal to the number â€˜Nâ€™.

Test your program with the following data and some random data:

Example 1:

INPUT:

N = 14

OUTPUT:

Prime pairs are:

3, 11

7, 7

Example 2:

INPUT:

N = 30

OUTPUT:

Prime numbers are:

7, 23

11, 19

13, 17

Example 3:

INPUT:

N = 17

OUTPUT:

Invalid input. Number is odd.

Example 4:

INPUT:

N = 126

OUTPUT:

Invalid input. Number is out of range.

```
import java.io.*;
class GoldBach
{
static int isPrime(int x)
{
int rem;
int count=0;
for(int i=1;i<=x;i++)
{
rem=x%i;
if(rem==0)
{
count++;
}
}
return count;
}
public static void main()throws IOException
{
BufferedReader br=new BufferedReader(new
InputStreamReader(System.in));
System.out.println("Enter the number");
int N=Integer.parseInt(br.readLine());
int res1=0;
int res2=0;
if(N>9 && N<50)
{
if(N%2==0)
{
System.out.println("PRIME PAIRS ARE:");
for(int i=3;i<=N;i++)
{
if(i%2!=0)
{
res1=isPrime(i);
for(int j=i;j<=N;j++)
{
if(j%2!=0)
{
res2=isPrime(j);
if(res1==2&&res2==2)
{
int temp=i+j;
if(temp==N)
{
System.out.println(i+", "+j); }
}
res2=0;
}
}
res1=0;
}
}
}
else
{
System.out.println("INVALID INPUT. NUMBER IS ODD"); }
}
else
{
System.out.println("INVALID INPUT. NUMBER OUT OF RANGE."); }
}
}
```

**Output:**

Enter the number

14

PRIME PAIRS ARE:

3, 11

7, 7