Numbers doesn't have the feature that you might be familiar with in Excel that allows you to do an operation on a column in that manner. The way to do it in Numbers is just basic:
Let's say that your original data is in Column A. In an auxiliary column, write:
Then Copy or Fill this expression to the rest of the auxiliary column. Copy the Auxiliary column, Edit > Paste Values over Column A.
This Auxiliary column can be any blank existing or inserted column.