I added a description of what should be copied (the formula), and that
should do it, I think. Your code should check  for empty cells in Column
A just fine.

Public Sub CopyDown()
LastRow = Range("A65536").End(xlUp).Row
For i = 1 To LastRow
If Range("A" & i).Value = "" Then
Range("A" & i - 1 & ":CB" & i - 1).Formula.Copy Destination:=Range
("A" & i)
End If
Next i
End Sub