function [val] = Reihe(N_max)

val = 0;

for k=1:N_max
    val = val + 1/k^2;
end

val2 = 0;
for k=N_max:-1:1
    val2 = val2 + 1/k^2;
end


fprintf('\nval  = %1.15f',val);
fprintf('\nval2 = %1.15f',val2);
fprintf('\nex   = %1.15f\n\n',pi^2/6);