Euler的圓周率

public class Pi{
public static void main(String[] args){
System.out.println("Euler(10)=" +Euler(10));
System.out.println("Euler(100)=" +Euler(100));
System.out.println("Euler(1000)=" +Euler(1000));
}
public static double Euler(int n){
boolean isPrime;
double sum = 1.0;
int count = 0;
int i = 3;
while(count < n){
isPrime = true;
for(int j=3; j<=Math.sqrt(i); j+=2){
if(i%j == 0){
isPrime = false; break;
}
}
if(isPrime){
if((i-1)%4 == 0) sum *= i / (double)(i+1);
else sum *= i / (double)(i-1);
count++;
}
i += 2;
}
return sum * 2;
}
}