prime_4.java

public static boolean isPrime(int number) {
    
    if (number < 2)
        return false;
    
    if (number == 2 || number == 3)
        return true;    
    
    if(number % 2 == 0 || number % 3 == 0)
        return false;
    
    int sqrt = (int) Math.sqrt(number);
    int dx = 4;
    
    for (int i = 5; i <= sqrt; i+=dx) {
        if (number % i == 0)
            return false;
        dx = - (dx - 6);
        
    }
    
    return true;
}