I have data in an excel spreadsheet. In one column, I have repeatative
entries. For example, the column looks like

aaaa
bbbb
aabb
aaaa
bbbb

etc.

The problem is that the column has some 20000 rows, and I need to find these
type of entries that are repeating again and again. For example in the above
case, what I am looking for is "aaaa, bbbb, aabb" that is all. In my real
example, I might have some 40 or 50 such different entries. It will take me
hours to go thru the column and find those. Plus manual error will be
unavoidable.