Unfortunately you can only sort either by ASCII code (letters) values, or numerically by value.   If you sort by ASCII values, your field must have certain restrictions placed on it.  Letter and number contents must adhere to fixed rules.  Text characters must be fixed length and be placed fixed relative to numeric values.   And numbers must always be formatted to a fixed length, for example a value of "1" must be formatted to occupy a space big enough for your largest number; which would be "000001" if you wont have more than six digits.    

If your field only contains numbers, and it's set for a numeric data type, you can enter values naturally, like "1", "356", etc.   If your data will contain both text components and numeric components, you probably want to separate them into two fields, one for text and one for the numeric part, then format your query to sort on both fields.   Alternately you do have the ability to specify a custom sorting function in a query that handles your specific needs.