幻影素数的问题，求帮助！！~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

题目：编写程序，找出介于a和b之间所有有构成幻影素数的数。所谓幻影数是指自身为素数，其反序数也是素数的数。例如107与701都是素数，所以107是幻影素数
我的代码：Private Sub Command1_Click()
Dim n As Integer, m As Integer, i As Integer
n = Val(Text1.Text)
m = Val(Text2.Text)
For i = n To m
   Call sub1(i)
   If prime(i) And prime(x) Then
    List1.AddItem i & "与" & x
   End If
Next i
End Sub
Private Sub sub1(ByVal x As Integer)
x = Val(StrReverse(CStr(x)))
End Sub
Function prime(ByVal k As Integer) As Boolean
Dim p As Integer
For p = 2 To Sqr(k)
   If k Mod p = 0 Then
   Exit Function
   End If
Next p
   prime = True
End Function
怎么最后X显示不出来