Private Sub Command1_Click()

Dim ch As String, s As String

Dim i As Integer, j As Integer

ch = Text1.Text

   For i = 1 To {#blank#}1{#/blank#} 

        j = Asc(Mid(ch, i, 1))

        If j > 96 And j < 123 Then

           s = s + Chr(j - 32)

        Else

         s = s + Chr(j)    

        End If

   Next

   {#blank#}2{#/blank#}

End Sub

Private Sub Command1_Click()

  Dim sjzs As Integer

  Dim rjzs As String

  sjzs = Val(Text1.Text)

  rjzs = ""

  Do While Int(sjzs / 2) > 0

    rjzs = Str(sjzs Mod 2) + rjzs

    sjzs = Int(sjzs / 2)

  Loop

  Label1.Caption = rjzs

End Sub

Private Sub Command1_Click()

Dim i As Integer, c As Integer, n As Integer

n = Val(Text1.Text)

c = 0

For i = 1 To n

If i Mod 3 = 0 Then c = c + 1

Next i

Label1.Caption = Str(c)

End Sub

运行该程序，在文本框Text1中输入20，单击命令按钮Command1，在标签Label1中显示的是{#blank#}1{#/blank#}。

请在下列程序代码的基础上按照要求设计该程序，完善程序中的划线部分。

Dim n As Integer, a1 As Integer, a2 As Integer, a3 As Integer

Function f(x as integer) As Boolean

 f=True

 For i=2 To Sqr(x)

   If x Mod i=0 Then {#blank#}1{#/blank#}

 Next i

End Function

Private Sub Command1_Click()

n={#blank#}2{#/blank#}

For a1=2 To n

 For a2=a1 To n

  For a3=a2 To n

   If{#blank#}3{#/blank#}And f(a1) And f(a2) And f(a3) Then

    List1.AddItem(Str(a1)+“ ”+Str(a2)+“ ”+Str(a3))

   End If

  Next a3

 Next a2

Next a1

End Sub

小明依据上述描述设计了如下VB程序，在Text1中输入矩阵的行数n (n≤10)，单击“生成”按钮Command1，在List1中显示n×n的螺旋矩阵。请回答下列问题：