Copy subset of rows from one sheet to another, based on value in column

Copy subset of rows from one sheet to another, based on value in column

I have a sheet with accounts, consisting of 3 columns:
Accountnr
Name
Category
This sheet is not nescessarily sorted on any column.The Category is one of
three possible values.
I want to fill a part of another tab with all the accountnrs of a certain
category. How can i do that? I have been looking at ARRAYFORMULA() but am
not sure that that will give me the solution.
Even though i do have fair amount of experience with Excel sheets (until a
few years ago), this is my first attempt at Google Sheets ;-)
Any advice is welcome
gr Bas