Count including up to n duplicates
 

Hello everyone,

Can anyone think of a formula that will give me a total count of items in a range of cells while counting up to, but not more than, six duplicates? For example, if A1:A20 includes two duplicates of a certain value, four duplicates of another value, eight duplicates of another value, and six unique values, it will return a "count" of 18 (2 + 4 + 6 + 6).

Thank you,

Dan B.