Well, I've finally worked out the way to calculate the magic number, but at least one digit must be wrong. But I still haven't worked out how to parse 17D, although I know what it must be (and this is the problem with the magic number I think). Also, 22A seems pretty impenetrable. Is the Tolkien reference just three letters backwards, and does it start with a girl's name (not to say too much!)? Thanks.