下列VB程序运行时，单击命令按钮Command1后，语句①被执行了次，文本框Text1中显示的内容是。

Private Sub Command1_Click()

  Dim a(1 To 5) As Integer.i As Integer

  a(1)＝1

  a(2)＝1

  For i＝3 To 5

    a(i)＝2*a(i－1)＋a(i－2)     ′语句①

  Next i

  Text1.Text＝Str(a(5))

End Sub