I needed a good autonumber formula recently and only found bad ones that easily get out of synch when entries are inserted, moved or deleted. Here is one for the next poor fool that works whereever you put it and does not get out of synch.

=IF(OR(ROW()=1,ISTEXT(INDIRECT(ADDRESS(ROW()-1,COLUMN())))),1,INDIRECT(ADDRESS(ROW()-1,COLUMN()))+1)