Thanks Derb

You should read everything John Derbyshire writes anyway, but I'd like to thank him for putting a puzzle I emailed him in his July Diary "Math Corner" here (it's on page 2, near the end, puzzle #3). Can you solve? (Bragging a bit, I got the puzzle in an easier version and, upon solving it relatively quickly, realized it could be made more difficult but still solvable, and sent that more difficult version in my email to Derb, which is the version he published.)