I have a column F with 71 rows in it. The cell value can vary between 1-26. What I am trying to do is have formula that will tell me what is 'missing' from col f to make a 'complete' series

For ex:
1
2
4
5
7
8
9
etc...through 26
in this case / example I am missing 3 and 6. If series is complete - (I have all 26 numbers), to display - all good. This column is not sorted.

Any ideas?