private void primeNumbersToolStripMenuItem_Click(object sender, EventArgs e)
        {
            basic b = new basic();

            b.MdiParent = this;
            b.Show();
        }
        private void factorialToolStripMenuItem_Click(object sender, EventArgs e)
        {
            basic b = new basic();

            b.MdiParent = this;
            b.Show();
        }