Number every Nth row

Re: Number every 99th cell

Try something like this...

Sub Test99()


    Dim lngLoop As Long
    
    For lngLoop = 99 To 10000 Step 99
        Cells(lngLoop, 1).Value = lngLoop / 99
    Next
    
    lngLoop = Empty
    
End Sub

Re: Number every Nth row

You didn't specify how the rows were to be numbered, so we assume row number.

Try this formula, copied down: =IF(MOD(ROW(),99)=0,ROW(),"")