richardson extrapolation method wrong

Why is this richardson extrapolation method wrong?

function D=f_richardson(f,n,h,x0)
D=zeros(n,n);
e=zeros(n);
for t=1:n
  D(1,t)=(f(x0+(2^(t-1))*h)-f(x0-(2^(t-1)*h)))/(2*((2^(t-1)*h)));
end
o=n-1;
for l=2:n
  for k=1:o
      D(l,k)=((2^(2*n-1))*D(l-1,k)-D(l-1,k+1))/(2^(2*n-1)-1);
  end
  o=o-1;
end
end