I understand that functions can only modify the cell they are called
from. However, if anyone has a solution to this problem, I would
greatly appreciate it.

A function F(N) does a vlookup in a table and returns a value.

If it cannot find N in the table, I want to add N to a list in
another table.

F() is called from an addin if that is relevant.

Any creative solution appreciated.

Thanks
Jeff Stryer