Fast way to check if column contains duplicates

Hello

Im trying to create a fast way to check if my column contains duplicates of my value. If it contains a duplicate, i want to return "yes" and if not "no".

I've managed to create a function like this but its to slow:

=IF(SUM.IF(B:B;B2508;B:B)>B2508;"Yes";"No")

This will check if the numer in B2508 has a duplicate.

Any way how to "improve" this?

Best Regards
/Richard