Caveat: The following question is mistaken and wrongly posted here.
A question was posted asking for all natural-number solutions $(a,b)$ of the equation $\surd a+\surd b=\surd2009$. It was near the top of my MSE home page of questions, but I couldn't find it a few hours later. The question came from a problem set in the British Mathematical Olympiad (presumably in 2009). It was tagged [contest-math] and I think with another tag—perhaps [elementary-number-theory] or [number-theory]. I searched generally for 2009, sqrt, surd, British, as well as using the specific route provided by the filter menu (taking care to untick any filter requirements other than the tag [contest-math]), with no results.
Apologies to all. The answer is that I found the problem elsewhere. Just my faulty memory attributed it to MSE and made up the details based on plausible presumption. I will leave the question up for a while, because I think that the replies in the comments are useful.