star_and_triangle.java

import java.util.Scanner;
public class TriangularStars {

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		Scanner input = new Scanner( System.in );
		String inputString="";
		do {
			System.out.print("How many star&triangle number do you want? (or 'quit')");
			input = new Scanner( System.in );
			if (input.hasNextInt())
			{
				int countRequired = input.nextInt();
				int countProduced = 0;
				int triangle_number = 0;

				for (int triangle_n = 1; countProduced < countRequired; triangle_n++) {
					triangle_number += triangle_n;
					if (isStarNumber(triangle_number)) { // if it's both triangle and star
						System.out.println(triangle_number); // print it
						countProduced++; // and increase count produced
					}

				}

			}
			else if (input.hasNext()) {
				inputString = input.next();
			}
		} while (!inputString.equalsIgnoreCase("QUIT"));
	}

	public static int determineStarNumber(int n)
	{
		return 6*n*(n-1) + 1;
	}

	public static boolean isStarNumber(int number)
	{
		// keep going while i is less than or equal number because
		// we know there isn't a star number less than it's position
		for (int i = 0; i <= number; i++) {
			if (determineStarNumber(i) == number) { return true; }
		}
		return false;
	}
}