Column B contains unique values which I need to copy down column A in groups of 17 (I only did groups of 4 for display purposes).

In the end, the real data has over 750 unique values in column B so when multiplied by the groupings of 17 would make over 13000 rows for column A.

Can this be done with a formula?

       -a-- -b--
   1   11aa 11aa
   2   11aa 11ac
   3   11aa 13ab
   4   11aa 13ae
   5   11ac     
   6   11ac     
   7   11ac     
   8   11ac     
   9   13ab     
  10   13ab     
  11   13ab     
  12   13ab     
  13   13ae     
  14   13ae     
  15   13ae     
  16   13ae