f[x_] := (1/(1 + (x^2)));
Nn = 40;  h = (10/Nn);
xa = 
        Table[-5 + i h, {i, 0, Nn}] // N;
ya = f  /@  xa ;
Txaya = Transpose[{xa, ya}];

g1 = ListPlot[Txaya, PlotJoined ->  True]

Export["Runge.dat", Txaya, "Table"]