Why is my random number generator returning negative values

I have made a very basic linear congruential generator (or at least I think I have) however it returns some crazy values including negative numbers. I cant for the life of me figure out why, any help very welcome. My code is below:

public static void main(String[] args) {
    Scanner scanner = new Scanner(System.in);
    long a = 252149039;
    int c = 11;
    long m =(long) Math.pow(2, 48);
    long seed = System.currentTimeMillis();
    System.out.println("How many Random numbers would you like to get?");
    int number = scanner.nextInt();
    for (int i = 0; i <= number;i++) {
        seed = ((a*seed)+c) % m;
        System.out.println(seed);
    }
    scanner.close();
}