Thank you for the follow-up shashank21j, your revision to the statement has been helpful, but I still have some questions about the way the question is worded and why.

1.Why must i+j+k not be equal to N and does this mean it can be greater than N?

2.Please define "lexicographic increasing order"

I for one agree that list comprehension in python is a fairly simple subject, the crux of this problem for me however, is bridging the communication gap/understanding the essance of the problem you're asking.

Many people who use your site are self taught in coding and do not have a formal discrete mathematics background.