I know I've done this before.. but for the life of me I can't figure out how.

I need to fill down on a column, however, the value changes every 4th
column.
Example:
Smith 1
2
3
4
Jones 1
2
3
4

And I need it to read

Smith 1
Smith 2
Smith 3
Smith 4
Jones 1
Jones 2
Jones 3
Jones 4

I recall a quick fill method... one of those fuzzy recollections at the
edge of my brain.. but I just can't grasp what it was? Can anyone help?

Thanks!