Public Class Form1

    Private Sub TextBox1_TextChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles TextBox1.TextChanged

    End Sub

    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        Dim n, i As Integer
        Dim sum As Integer
        sum = 0
        n = CInt(TextBox1.Text)
        For i = 1 To n
            sum = sum + i ^ 2
        Next
        TextBox2.Text = sum
    End Sub

    Private Sub TextBox2_TextChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles TextBox2.TextChanged

    End Sub
End Class