Thanks Frodo, I've tried to update to site with the tips you mentioned (I've also descibed a bit about factoring in my SoB guide - please proofread!).

BTW both http://www.seventeenorbust.com/largesieve/ and http://www.seventeenorbust.com/sieve say "k = one of the 11 left". Maybe one of the mods should change this?

OH