This is a puzzle that I've worked on-and-off for quite a few years, but not being a competent coder, I haven't worked out a definitive solution. I suspect the 1st part is impossible but haven't proved it and the subsequent iterations are enough of a challenge that I thought I'd include it all here.
Create a 5x5 grid of letters containing the English words for each of the 1st 18 counting numbers (i.e. 'one, two, three, ..., seventeen, eighteen) to be found in the style of Boggle. I'm fairly sure (but not positive) that this cannot be done - however, the numbers 'one' through 'seventeen' can be done as can 1-18 except 'five' or 1-18 except 'fifteen'.
So the challenge is either to be the first to find 1-18 or to conclusively prove that it's impossible. If it's the latter then post your solutions to 1-17, 1-18 less 5, 1-18 less 15, etc.