Are these recursive sequences convergent? Fix an integer $k > 1$. Suppose $a_1,\ldots,a_k > 0$ and for $n > k$ we define
$$a_n = 1/a_{n-1} + 1/a_{n-2} + \ldots + 1/a_{n-k}$$
Are these recursive sequences always convergent for any $k$ and any initial values? It seems like if they are,  then the limit must be $\sqrt{k}$.
 A: Let $q>0$.
If all of $a_{n-k},\ldots,a_{n-1}$ are $<q\sqrt k$, then $a_n>q^{-1}\sqrt k$.
And if all of $a_{n-k},\ldots,a_{n-1}$ are $>q\sqrt k$, then $a_n<q^{-1}\sqrt k$.
And if all of is $<q\sqrt k$, then clearly $a_n>q^{-1}\sqrt k$.
So define $b_n:=|\ln \frac {a_n}{\sqrt k}|$. By what we have just shown, $$b_n\le\max\{b_{n-1},\ldots, b_{n-k}\},$$ so that the sequence $b_n$ is nonincreasing (apart from possibly the initial $k$ terms). Being bounded from below by $0$, the sqeuence $b_n$ converges to some $b\ge 0$.
Let $q=e^b$. Let $\epsilon>0$. Then for almost all $n$, we have $$\tag1\frac1{1+\epsilon}q\sqrt k<a_n<(1+\epsilon)q\sqrt k$$ or $$\tag2\frac1{1+\epsilon}q^{-1}\sqrt k<a_n<(1+\epsilon)q^{-1}\sqrt k.$$ If among $k$ consecutive terms $a_{n-k},\ldots, a_{n-1}$, $r$ obey $(1)$ and $k-r$ obey $(2)$, we obtain
$$\tag3 \frac1{1+\epsilon}(\tfrac rq+(k-r)q)\sqrt k<a_n<(1+\epsilon)(\tfrac rq+(k-r)q)\sqrt k$$
If $b>0$  (and hence $q>1$), we can pick $\epsilon$ so small that $(3)$ is  compatible with $(1)$ or $(2)$ only if $r=0$ or $r=k$. But as seen in the first paragraph, $k$ small values are followed by a big value and vie versa, i.e., we cannot always have $r=k$ or $r=0$. From this contradiction, we conclude $b=0$.
