public Form1()
{
    InitializeComponent();
}
 
public static Brush aBrush = (Brush)Brushes.White;
 
public int current_x = 200;
public int current_y = 200;
public static string path_collect = "";
public int cur_step = 1;
public static int Current_Direction = 0;
public bool first_turn = false;
public int count = 5;
public int skip_at = 7;
public int skip = 3;
public int diag_count = 4;
public int prime_count = 2;
double percentage = 100.0;
 
protected void Move()
{
    cur_step += 1;
    Graphics g = this.CreateGraphics();
    if (cur_step == skip_at)
    {
        diag_count += 1;
        if (isPrime(cur_step))
        {
            aBrush = (Brush)Brushes.Red;
            prime_count += 1;
        }
        else
            aBrush = (Brush)Brushes.Black;
    }
    else
        aBrush = (Brush)Brushes.Black;
 
    if (Current_Direction == 0)
    {
        g.FillRectangle(aBrush, current_x + 2, current_y, 2, 2);
        current_x += 2;
        path_collect = "→";
    }
    else if (Current_Direction == 3)
    {
        g.FillRectangle(aBrush, current_x, current_y + 2, 2, 2);
        current_y += 2;
        path_collect = "↓";
    }
    else if (Current_Direction == 2)
    {
        g.FillRectangle(aBrush, current_x - 2, current_y, 2, 2);
        current_x -= 2;
        path_collect = "←";
    }
    else if (Current_Direction == 1)
    {
        g.FillRectangle(aBrush, current_x, current_y - 2, 2, 2);
        current_y -= 2;
        path_collect = "↑";
    }
 
        percentage = Math.Round((System.Convert.ToDouble(prime_count) 
            / System.Convert.ToDouble(diag_count)), 2);
    label1.Text = "Number " + cur_step + "   " + path_collect 
        + " Diag " + diag_count + " Primes "
        + prime_count + " Percent " + String.Format("{0:P2}", percentage) ;
 
    if (cur_step <= 3)
        Turn();
    if (cur_step == 5)//2
        Turn();
    if (skip_at == cur_step)
    {
        skip_at += skip;
        if (first_turn == false)
            first_turn = true;
        else
        {
            first_turn = false;
            skip += 1;
        }
        Turn();
    }
    count += 1;
}
 
private void bntGo_Click(object sender, EventArgs e)
{
    bntGo.Enabled = false;
    backgroundWorker1.RunWorkerAsync();
}
 
protected void Turn()
{
    if (Current_Direction == 3)
        Current_Direction = 0;
    else
        Current_Direction += 1;
}
private void backgroundWorker1_DoWork(object sender, DoWorkEventArgs e)
{
    while (true)
        Move();
}
public static bool isPrime(int n)
{
    if (n == 1)
        return false;
    if (n == 2)
        return true;
    for (int i = 2; i < n; ++i)
    {
        if ((n % i) == 0)
            return false;
    }
    return true;
}
private void Form1_Paint(object sender, PaintEventArgs e)
{
    int x = 10;
    int y = 10;
    for (int i = 1; i < 41; i++)
    {
        for (int j = 1; j < 41; j++)
        {
            e.Graphics.DrawEllipse(Pens.Black, x * i, y * j, 1, 1);
        }
    }
    Graphics g = this.CreateGraphics();
    g.FillRectangle(aBrush, current_x, current_y, 2, 2);
}