OK. Until a short while ago (when I entered all my answers the right way round, having found out why the first guess was wrong) I was with the cross crossWORD people. It's taken me until now (with time off to do 4076) in bits and pieces to crack this thing. I did it the spreadsheet way (huge respect to ruthrobin for doing it without) and kept hitting a brick wall until I realised I'd entered one (one!) of the clues with a * where it should have been a +. I found this site
http://www.algebra.co...r-any-number-1.solver handy for doing the 23's, I'd forgotten how to find factors. When the light dawned, I was transformed from hating all you smug b...rainiacs who had cracked it to being a massive admirer of the Arden's skill and that incredible reversible number at the top. I still think it's a hell of a slog, and I'm still not sure what an arithmetic puzzle is doing in a words competition, but I confess 4076, though also brilliant, seemed a little tame by comparison. I have 9 spoiled grids littering my study. Can anyone beat my record?