/// <summary>
        /// Gets the column letter of a given column number.
        /// </summary>
        /// <param name="columnNumber">The column number to translate into a column letter.</param>
        /// <param name="trimToAllowed">if set to <c>true</c> the column letter will be restricted to the allowed range.</param>
        /// <returns></returns>
        private static string NaiveGetColumnLetterFromNumber(int columnNumber, bool trimToAllowed = false)
        {
            if (trimToAllowed)
            {
                columnNumber = XLHelper.TrimColumnNumber(columnNumber);
            }

            columnNumber--; // Adjust for start on column 1
            if (columnNumber <= 25)
            {
                return(letters[columnNumber]);
            }
            var firstPart = (columnNumber) / 26;
            var remainder = ((columnNumber) % 26) + 1;

            return(NaiveGetColumnLetterFromNumber(firstPart) + NaiveGetColumnLetterFromNumber(remainder));
        }