You could incorporate the row function. If, for example, this began in row
2, instead of the 2, enter =3*(row()-2)+2. In row 2 that evaluates to 2.
But copy it down to row 3 and it evaluates to 5, etc.

"Kia" wrote:

If I have =VLOOKUP(date,data,2) and in the next cell down I want
=VLOOKUP(date,data,5) so the col_index_num increments by 3 each time how
would I go about doing this so that it can be copied down instead of editing
each line by hand?

Many Thanks in advance