code: import java.awt.*;
  import javax.swing.*;
  
  public class LargeUlamSpiral extends JPanel {
  
      public LargeUlamSpiral() {
          setPreferredSize(new Dimension(605, 605));
          setBackground(Color.white);
      }
  
      private boolean isPrime(int n) {
          if (n <= 2 || n % 2 == 0)
              return n == 2;
          for (int i = 3; i * i <= n; i += 2)
              if (n % i == 0)
                  return false;
          return true;
      }
  
      @Override
      public void paintComponent(Graphics gg) {
          super.paintComponent(gg);
          Graphics2D g = (Graphics2D) gg;
          g.setRenderingHint(RenderingHints.KEY_ANTIALIASING,
                  RenderingHints.VALUE_ANTIALIAS_ON);
  
          g.setColor(getForeground());
  
          double angle = 0.0;
          int x = 300, y = 300, dx = 1, dy = 0;
  
          for (int i = 1, step = 1, turn = 1; i < 40_000; i++) {
  
              if (isPrime(i))
                  g.fillRect(x, y, 2, 2);
  
              x += dx * 3;
              y += dy * 3;
  
              if (i == turn) {
  
                  angle += 90.0;
  
                  if ((dx == 0 && dy == -1) || (dx == 0 && dy == 1))
                      step++;
  
                  turn += step;
  
                  dx = (int) Math.cos(Math.toRadians(angle));
                  dy = (int) Math.sin(Math.toRadians(-angle));
              }
          }
      }
  
      public static void main(String[] args) {
          SwingUtilities.invokeLater(() -> {
              JFrame f = new JFrame();
              f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
              f.setTitle("Large Ulam Spiral");
              f.setResizable(false);
              f.add(new LargeUlamSpiral(), BorderLayout.CENTER);
              f.pack();
              f.setLocationRelativeTo(null);
              f.setVisible(true);
          });
      }
  }
  