I want to check if $$\lfloor \left( \sum_{k=n}^{2n}{\frac{1}{F_{2k}}} \right) ^{-1} \rfloor =F_{2n-1}~~(n\ge 3)(*)$$ where $\lfloor x \rfloor$ is a floor function. Fibonacci sequence is defined by $F_1=1$, $F_2=1$, $F_{n+1}=F_n+F_{n-1}~(n\ge 2)$. Then we can get $$F_n=\dfrac{\alpha ^n-\beta ^n}{\sqrt{5}}$$ where $\alpha=\dfrac{1+\sqrt{5}}{2}$ and $\beta=\dfrac{1-\sqrt{5}}{2}.$ The following are some of my attempts: > For some example: > > $n=3$, the left hand is $5$, the right hand is $5.$ > > $n=4$, the left hand is $13$, the right hand is $13.$ > > $$\vdots$$ > > $n=15$, the left hand is $514229$, the right hand is $514229.$ > > It is all true. But as $n$ increases, the order of magnitude grows > very rapidly. > > I ask one of my good friends to ues a Python program to check $(*).$ > He says it is true for $n\le 35$. When $n=36$, the Python says it is not ture, But when $n= 37$, it is true again. > > Thus I change one way and I ask my fiend to use a Python program to > check $$\left( \sum_{k=n}^{2n}{\frac{1}{F_{2k}}} \right) ^{-1} > =F_{2n-1}~~(n\ge 3)(**).$$ > > Then the program shows it is true at least for $31\le n\le 51.$ > >But as you see, the left hand of $(**)$ is a decimal and the right hand of $(**)$ is an integer. So I donot know if it is because the order of magnitude on the left hand of $(*)$ is growing very fast, $(*)$ becomes not true due to some computer shortcomings. Finally I wonder if $(*)$ is true or false? Any help and references are greatly appreciated. Thanks!