Java The Van Eck sequence

import java.util.*;


public class Main {

    private static final int DEFAULT_STARTING_NUMBER = 0;
    private static final int DEFAULT_STARTING_POSITION = 0;

    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int maxNumsToPrint;
        int[] nums;

        try {
            System.out.println("Enter a number:");
            maxNumsToPrint = scanner.nextInt();
            nums = new int[(int) Math.sqrt(maxNumsToPrint * maxNumsToPrint)];
        } catch (InputMismatchException ime) {
            System.out.println("The thing you've entered isn't a number");
            return;
        }

        for(int i = 0; i <= nums.length - 1; i++){
            nums[i] = -1;
        }

        nums[DEFAULT_STARTING_POSITION] = DEFAULT_STARTING_NUMBER;
        System.out.println(nums[DEFAULT_STARTING_POSITION]);

        for(int i = 0; i < nums.length - 1; i++){
            if(!isUnique(nums, nums[i])){
                nums[i + 1] = i - secondLastIndexOf(nums, nums[i]);
                System.out.println(nums[i + 1]);
            }
            else {
                nums[i + 1] = 0;
                System.out.println(0);
            }
        }

    }

    private static boolean isUnique(int[] intArr, int n){
        boolean seenOnce = false;

        for(int i = 0; i <= intArr.length - 1; i++){
            if(intArr[i] == n){
                if(seenOnce){
                    return false;
                }
                seenOnce = true;
            }
        }
        return true;
    }

    private static int secondLastIndexOf(int[] intArr, int numToSearch) {
        int counter = 0;
        boolean seenOnce = false;

        for (int i = intArr.length - 1; i >= 0; i--) {
            if (intArr[i] == numToSearch) {
                if(seenOnce){
                    counter = i;
                    break;
                }
                seenOnce = true;
            }
        }

        return counter;
    }
}