In their paper "moyenne de certains fonctions arithmétiques sur les entiers friables", Tenenbaum and Wu proved that for the case of the function $\beta$ which is the indicator function of integers sums of two squares, it exists a continuons function on [0,1] $\lambda$ such that $\lambda(0)>0$ and $$\sum_{n \leq x} \beta(n)= \int_0^{1/2} x^{1-t} \frac{\lambda(t)}{\sqrt{t}} dt+O\left(\frac{x}{L(x)^c}\right)\quad (x\geq 3).$$ Where $$L(x)=\exp(\frac{\log(x)^{3/5}}{\log_2(x)^{1/5}})$$ and $c$ is a suitable positive constant. This result is due to Selberg-delange method. My question concerns an explicit values of $\lambda$ and This to find a good bound for the sums of $\beta(n)$ less or equal to $x.$ Many thanks in avance.