ASP.Net AJAX Line Chart control : Display all values in on X Axis

hello, I work with a tank of visual studio when I click to display the graph he shows not all points on the X axis

for example the table nbr_num_semaine_av contains values in order

(18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,1,2,3,4)

but the graph shows on the X axis only that 18, 38, 41

 for (int k = 0; k < semaine.Count(); k++)
        {
            Chart4.Series["Nombre de points terminés"].Points.AddXY(nbr_num_semaine_av[k], nbr_points_Termin[k]);
            Chart4.Series["Nombre Total d'element"].Points.AddXY(nbr_num_semaine_av[k], nbr_element.Count());
        }
Chart4.Series["Nombre de points terminés"].ChartType = SeriesChartType.Line;
        Chart4.Series["Nombre Total d'element"].ChartType = SeriesChartType.Line;
  Chart4.Series["Nombre de points terminés"].IsXValueIndexed = true;
  Chart4.Visible = true;