Source code C#

namespace ConvertExcelColumnName
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }
        class ColumnExcel
        {
            public int Number { get; set; }
            public string ExcelColName
            {
                get
                {
                    return GetExcelColumnName(this.Number);
                }
            }

            private string GetExcelColumnName(int columnNumber)
            {
                string columnName = "";

                while (columnNumber > 0)
                {
                    int modulo = (columnNumber - 1) % 26;
                    columnName = Convert.ToChar('A' + modulo) + columnName;
                    columnNumber = (columnNumber - modulo) / 26;
                }

                return columnName;
            }
        }

        private void Form1_Load(object sender, EventArgs e)
        {
            var listData = new List<ColumnExcel>();
            for (int i = 1; i < 2000; i++)
            {
                var colExcel = new ColumnExcel();
                colExcel.Number = i;
                listData.Add(colExcel);
            }
            dataGridView1.DataSource = listData;
        }

    }
}