I am seeking help in my attempt to formulate a proof to disprove the following.
For a measurable function $f$ on $[1,\infty )$ which is bounded on bounded sets, define $a_n= \int_{n}^{n+1}f$ for each natural number $n$. Is it true that $f$ is integrable over $[1,\infty )$ if and only if the series $\sum _{n=1}^{\infty }a_{n}$ converges ?
I strongly suspect this to be false and could prove that if the series converged absolutely then $f$ is integrable over $[1,\infty )$ but i am unsure how to extend this to answer the question based on conditional convergence of the series.
Any help would be much appreciated.