more challenge sequences needed

[Rainer Rosenthal]

> I have participated in all of the previous contests, 
> and requirement 4 refers only to the feasibility of 
> a solution--not the optimality.  It's okay if optimality 
> is hard to prove.  But feasibility should be easy to 
> check so that the contest administrator can quickly 
> give scores for solutions submitted by the contestants.  

Hello Rob,

nice to hear that. Sounds like rising the chance for A004137,
because feasibility is very easy to check - as I wrote:
"While on the other hand it is easy to show that such a 
 set {x1,...x_m} doesn't have holes in its differences."

Best regards,
Rainer Rosenthal
r.rosenthal at web.de