List without repetitions

I know there's like a million posts on here with this, I can't seem to find any, I'll keep looking in the meantime though.

Looking to list duplicates in a column without spaces.

I apologize because I'm sure this is a bazillionate post, I'll keep looking in the meantime.

mew...

For a list entered into D2:D20, with D1 as the column heading

These ARRAY FORMULAS must be committed with CTRL+SHIFT+ENTER,
instead of just ENTER:

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Copy D3 into D4 and down through as many cells as you need to cover all possible unique items

Is that something you can work with?

Checking it now.
I know how to filter out duplicate results, I wanted to get my hands on a code that will accomplish that without having to delete the duplicate cells. I'll see how this works.

Thanks.

mew.

Edit:
Lists all individual values correctly, without duplicates. I already know how to isolate duplicates, so I should be able to combine the two and come out with a unique list of my duplicate list, thanks again.

and

mew.

again.

Edit:
Uploaded example worksheet for others reference. Note that all formulas in column AN are arrays, and that AN2 differs from the rest of AN, as given by Ron Coderre's example.