Is there a way to write a count forumla so that you can count the number of
cells, but omit cells with the same information?

For example...I have a list that has page numbers and actions that were done
on those pages.

Can I write a formula that will count the cells that contain the page
numbers, but only count each page number once?

Say I have two cells that have page 6, one that has page 7 and four that
have page 8. They are all in the same column, but I only want to count the
three pages, not the occurrences of the page numbers.

I hope that this is clear.
Thanks.