I had a similar problem and i did the following
1. Copy all data from Col A and paste into a new Col C
2. Copy all data from Col B and paste it Col C. (Below the Last used cell)
by doing this you will have all the Nos in one Col . i.e. Col C

3.Now sort the Col C use ascending
by doing this all the repeating Nos will be seen just below each other

4. in Col D. Type Formula =C1-C2
Copy - Drag this Formula to All Cells in Col D

5. Finally Use a Filter for Col D - select 0 (Zero)
This will only show you row's which has (Zero) in Col D
Delete all these Rows.

Remove the filter and you will have Single Entry of Data in Col C

Long Method but it may help

"schreibdave" wrote:

Hi

I need help creating a formula that would do the following: I have two
columns of numbers - they are customer #s. Some of the numbers are in both
columns, others are in one column. How would I set up a formula to identify
which numbers are in one coumns but not in the other? Thanks a lot.