// (1 = A, 2 = B...27 = AA...703 = AAA...)
public static string GetColNameFromIndex(int columnNumber)
{
	int dividend = columnNumber;
	string columnName = String.Empty;
	int modulo;

	while (dividend > 0)
	{
		modulo = (dividend - 1) % 26;
		columnName = Convert.ToChar(65 + modulo).ToString() + columnName;
		dividend = (int)((dividend - modulo) / 26);
	}

	return columnName;
}

// (A = 1, B = 2...AA = 27...AAA = 703...)
public static int GetColNumberFromName(string columnName)
{
	char[] characters = columnName.ToUpperInvariant().ToCharArray();
	int sum = 0;
	for (int i = 0; i < characters.Length; i++)
	{
		sum *= 26;
		sum += (characters[i] - 'A' + 1);
	}
	return sum;
}