The billboard shown above is part of a recruiting campaing of Google. I am far from smart enough to solve this problem, and it this moment I haven’t got any plans to move to the United States. But I am interested in the solution, so for the moment I wait until somebody has solved this problem, and publishes it on internet. After that, I will be able to find it throught Google.
**[Update 2004.07.14]**: Google already gives some answers. The best discussion about the answer —7427466391.com— is found at the FogCreek forum.