Thanks for the reference, but NOT IT!
It was as I described, with the “trick” of the programming revealed at the end. I looked through the whole Arthur Clarke Short Stories compendium, and many of these are very short and fit the template of a contrived story to illustrate or exploit a simple concept, very much as I recall this one, but none of them came near to the actual story line.
... NOT INSANE!
Can you remember a line in it? An odd name, a quote? A unique planet name or creature, or vehicle?
Er, I was responding to struwwelpeter’s #3 about the “offdog.”