Fourier series of a function(B function (B spline) are given by: $$s(x)=\sum_{j=-\infty}^{\infty}sinc[\pi\frac{j}{K}]^{p}exp[2\pi s(x)=\sum_{j=-\infty}^{\infty}\operatorname{sinc}\Bigl[\pi\frac{j}{K}\Bigr]^{p}\exp[2\pi ijx]$$