Dennis is using numbers for a football play which is the combination to Mr. Wilson's safe, So Mr. Wilson and Henry get Dennis so confused that he forgets the combination. Then Mr. Wilson forgets it. Now they are in a real mess because Mr. Wilson has something very important locked in the safe. So Mr. Wilson tries everything including trying to hypnotize Dennis so he can remember the combination. He ends up hypnotizing himself and remembers the combination at last. (thetvdb.com)