проверка простые числа или не простые

Private Sub CommandButton1_Click()
For X = 0 To 15
y = X * X + X + 17
For a = 2 To X - 1
If X = Int(X / a) Then
MsgBox "число не простое"
ElseIf X <> Int(X / a) Then
MsgBox "простые числа:" & y
End If
Next a
Next X
End Sub

Private Sub CommandButton1_Click()
Dim x As Integer, y As Integer, i As Integer, j As Integer, k As Integer, pr As Integer
Dim z1 As String, z2 As String, kol As Integer
z1 = "Простые числа: "
z2 = "Непростые числа"
kol = 0
For x = 0 To 15
    y = x ^ 2 + x + 17
    pr = 1
    k = Int(Sqr(y))
    For i = 2 To k
        If y Mod i = 0 Then
            pr = 0
            Exit For
        End If
    Next i
    If pr = 1 Then
        z1 = z1 & y & " "
        Else
        z2 = z2 & y & " "
        kol = ko + 1
    End If
Next x
If kol = 0 Then z2 = z2 & " НЕТ"
MsgBox z1 & Chr(13) & Chr(13) & z2
End Sub