Currently I am reading Pour-El and Richard Computability in Analysis and Physics.
In Chapater $0$, they give a definition of computable double sequence.
Definition: A double sequence will be called computable if it is mapped onto a computable sequence by one of the standard recursive pairing functions from $\mathbb{N}\times\mathbb{N} $ onto $\mathbb{N}.$
However, I have trouble understanding the definition. My question is about verifying a certain example.
Question: Let $$x_{nk} = \frac{k}{k+n+1}.$$ Is the double $\{x_{nk}\}$ above is computable?