function [zn]=esround2(N)
zz=2;
zn=[zz];
for n=2:N
    zz=2^(n-0.5)*sqrt(1-sqrt(1-4^(1-n)*zz^2));
    zn=[zn;zz];
end
figure(1);
semilogy((2:N+1),abs(zn-pi),'*');
xlabel('n'); ylabel('|z_n-pi|')
% hold on
% plot((2:N+1),pi*ones(size(zn)))
