In Excel, create a list of the numbers 1 to 3 hundred, starting in Cell A2
and going down the column.  In cell A1, insert the word Number.  Then save
this file and use it as the data source for a formletter type mail merge in
which you insert the merge field number in the desired places on the page
and before the second one, insert a <<Next Record>> field.  Then execute the
merge to a new document and you will have what you want.