Function convert(i As Long) As String
    
    Dim num As Long
    Dim str As String
    
    str = Chr(((i - 1) Mod 26) + 65)
    num = (i - 1) \ 26
    
    Do While num <> 0
        
        str = Chr(((num - 1) Mod 26) + 65) & str
        num = (num - 1) \ 26
        
    Loop
    
    convert = str
    
End Function


Sub Macro1()
    
    Dim i As Long
    
    For i = 1 To 5000
        Cells(i, 1) = i
        Cells(i, 2) = convert(i)
    Next
    
End Sub