public class Number {

    private int number;
    static final HashSet<Integer> pSet = new HashSet<>();
    static {
        pSet.add(2);
    }

    public Number(int n) {
        number = n;
    }

    public boolean isPrime() {
        boolean out = true;
        if (number == 1) { return true; }
        if (pSet.contains(number)) { return true; }
        for (int i : pSet) {
            if (number%i == 0) {
                out = false;
                break;
            }
        }
        if (out) { pSet.add(number); }
        return out;
    }
}