判断是否为素数！请大神指教！！

Private Function kk(x As Long) As Integer
Dim i As Integer
For i = 2 To x - 1
If x Mod i = 0 Then
Exit For
End If
Next i
If i >= x Then
kk = 1
Else
kk = 0
End If
End Function
Private Sub Command1_Click()
Dim x As Long
x = InputBox("enter data:")
If kk(x) = 0 Then
Print x; ":不是素数"
Else
Print x; ":是素数"
End If
End Sub
为什么上面的function那里i>=x呢？for 循环那里 i最大也应该是X-1啊 怎么会大于等于X呢？？