How can I count the number of blank cells between
the row above and the last nonblank row above, if
the cell in this row is nonblank?

That is, the count is one or more only in the first
nonblank cell following one or more blank cells.

For example, suppose A1:A2 are nonblank, A3:A5
are blank, and A6:A9 are nonblank. I want B6 to
count 3 and B10 to count 4. All other cells in B:B
should be blank (or zero).

I know I can do this easily in VBA.

Is there some way to write a cell formula that only
uses built-in Excel functions -- preferrably not even
add-ins?