How do I minus away repeated combinations?

My question has a little relation to Digital Logic design. But what I want to ask is how I could calculate through the use of combinatorics counting techniques.

Given a boolean function F(A,B,C,D,E) = CD' + ABD'E' + DE + A'BE

How do I find the number of unique minterms through the use of combinatorics? First, I listed out a table of bit string to visualise:

Code:

`A B C D E`

x x 1 0 x

1 1 x 0 0

x x x 1 1

0 1 x x 1

"x" are the possibility of being a 1 or 0.

Then I had 2^2 + 2^1 + 2^3 + 2^2 = 18, which is the permutation of the terms. But this includes the repeated terms which I don't know how to minus away to get only the unique number of minterms.

How do I find out the number of repeated minterms and minus from 18?

I am sorry if I've posted this in a wrong section.

Thanks!