I wrote:
> > (What if we require all the numbers to be rational? I haven't figured this
> > part out yet.)
>
> It can be done with 4 numbers:
More generally, it can be done with n numbers if and only if n >= 4. Consider:
0: {}
5: {-18, -1/36, 1/36, 6, 12}
6: {-6, -1/6, 1/6, 1, 2, 3}
7: {-63, -2/21, -1/21, -1/42, 1/6, 21, 42}
and append k different copies of {-a/b, -b/a, b/a, a/b} to the solution
of cardinality n - 4k.
Best wishes,
Adam P. Goucher
