Elap, the setter of this excellent mathematical puzzle, posted this to Answerbank:
TO WHOM IT MAY CONCERN
If anyone divulges the secret, they will be stripped naked, hung upside-down, and beaten on the soles of their feet with a dead carp.
YOU HAVE BEEN WARNED...
Can we respect his wishes and not give away the secret, please, for once. If you are stuck, you can email me but Elap clearly does not want the secret posted.