Public Class Form1

    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        Dim fileContents As String
        fileContents = My.Computer.FileSystem.ReadAllText(Application.StartupPath & "\Test2.txt")
        Dim row() = Split(fileContents, vbNewLine)

        Dim str1 = ""
        For i As Integer = 0 To Val(row(0))
            If row(i) = "" Then Exit For
            Dim k = Val(row(i))
            For j As Integer = k - 1 To 1 Step -1
                If f(k - j) = True And f(k - (k - j)) = True Then  '條件：兩個都是質數
                    str1 = str1 & k - j & " " & k - (k - j) & vbNewLine
                    Exit For
                End If
            Next
        Next

        My.Computer.FileSystem.WriteAllText(Application.StartupPath & "\result2.txt", str1, False)

        End
    End Sub

    Function f(ByVal n) '質數判斷
        Dim c = 0
        Dim a = False
        For i As Integer = 1 To n
            If n Mod i = 0 Then c = c   1
        Next
        If c = 2 Then a = True
        Return a
    End Function
End Class