I'm asking the next thing:
If we have a rational conditionally convergent series: $$\beta=\sum_{i=0}^\infty q_i \; \; \; ({q_i}\in\Bbb Q)$$ Then we know thanks to Riemann that it may be rearranged to converge to any value at all, but here's my question: ¿if there's a rearrangement $(q_{\sigma(n)})_{n}$, how can we know that $\sum_{i=0}^\infty q_{\sigma(i)}$ converges to $\beta$? (you can impose conditions on sigma if you want).