Counting blanks in non-adjacent cells

Okay, try this in either A2 or B2:

Formula:

=SUMPRODUCT((MOD((COLUMN($C2:$DW2),3)=0)*($C2:$DW2=""))

Adjust the range to suit (I guessed at DW), then copy down.

If your range is constantly increasing, perhaps you can use a much bigger range and if you only fill the headers in when the columns are used, then you could have another test to see if row 1 cells are empty - a big range will slow down the calculation speed, however.

Hope this helps.

Pete