> sum(1/(4*(2*k-1)^2-1),k=1..infinity);

> plot(4*sin(x/2)+
16/Pi*sum(sin((2*k-1)*x)/(2*k-1)/(1-4*(2*k-1)^2),k=1..10),
x=0..10*Pi,color=black,thickness=2);

>