get the value of prompt in Presentation variable.( you can set this up in the prompt)
Use the presentation variable to divide column C in your report.
unless you mean Column C to be made to N equal columns or rows.
Create a table with three columns. Column1 - dummy Key, column2 - parts column, 3 - unique identifier
table will looklik
col1 col2 col3
a 1 1
a 2 2
a 2 3
a 3 4
a 3 5
a 3 6
now create a columns in the fact table which has the measure which needs to be split to n parts and populate it with only 'a'
join this column with col1. use col2 for prompt (this is a must or else you query will go on a Cartesian join and will crash the system. There should always be a filter on col2).
in the report
Add col C, col2, col 3 . then divide col c by col2. hide col3.( col3 is added in order to avoid groupby col2)
you will get the split in rows.
Use a pivot table to make it to columns.