Yes!
I heard about it a while ago - but never gave serious thought - as those problems are mostly mathematical - and usually do not
test cleanliness of code and/or design (since solution is judged based on correctness and efficiency alone - usually 'good' solutions are very tightly coupled to problem statement and with very little scope to modify/extend).
But that apart, from pure mathematical coding point of view, those are very nice puzzle (and let me warn you - very additive! I just wanted to have a look at them a couple of days back - and before I knew I finished around 5 issues within half night

).
By the way, is there any such project/website to check code cleanliness or design principles (e.g. given a problem statement - can coder write a 'clean code', follow SOLID/TDD, can he/she identify which design
pattern(s) would be most suitable for it - so that minimal changes would be needed for further requirements etc.)?
Thanks in advance!
Regards,
Anayonkar Shivalkar (SCJP, SCWCD, OCMJD, OCEEJBD)