Numbers with anticlosed sets of non-squares

[jens at voss-ahrensburg.de]

I wrote


> As a note: It is not too hard to show that no number divisible by 4
> can appear in the list.

Addendum: Neither is it too hard to show the following: If u is an odd
number such that 2*u is in the list, then so is u itself.

With this, one only needs to show that 3 and 5 are the only odd numbers
in the list.

Regards,
Jens