This was first posted to SE, but now I think its better to be posted here.
For what positive real numbers $\alpha$, the sequence $a_n = \frac{[n\alpha]}n $$a_n = \frac{\lfloor n\alpha\rfloor}n $ is (not necessary strictly) increasing for sufficiently large indexes ? ($[x]$$\lfloor x\rfloor$ is the integer part of $x$).