Please try change the datatype of the column to string. I know you have also tried converting the column to string but was using a calculated field or through default data type? Can you post some of those account numbers here so that I can try that out? I am sure that number data type is creating a problem for you.
In tableau, please try changing the data type of the column as show below. This will CountD all the items in the column.
I also want to know the what is the source of data (excel,access or sql server etc)? If you have text, number and special characters in your column then by default it should be string and not a number. If possible change the datatype of the column at the DB level if it doesn't work at tableau level.
Let me know if that helps.
Thanks and Regards,
The source of the data is excel. I tried changing the data type of the column like your example and it did the same thing as when I changed the data type on the data source page. In excel the data type was number. I tried changing it to text, but it didn't seem to affect anything on tableau by doing that. Here are some examples of the account numbers: