Sub f()
Dim x, y, z
For a = 1 To 2000
For b = 1 To 2000
x = 0
y = 0
For c = 0 To 500
z = x
x = x ^ 2 - y ^ 2 + a / 500 - 2
y = 2 * z * y + b / 500 - 2
If x ^ 2 > 9 Then
Exit For
End If
Next c
Cells(b, a).Interior.Color = (x + y) * 99
Next b
Next a
End Sub

9 28