I already know that a regular n-sided polygon is constructible with
straighedge and compass only if
n=2^k*p_1*p_2*p_3*...
where k is any nonnegative integer and the p's are distinct Fermat primes.
I
have also seen constructions for other low-order regular polygons that use
a
trisection device in the construction. (Conway and Guy's book "On Numbers
and Games" has such constructions.)
My question is: Are a compass, ruler and trisection device sufficient to
construct any n-sided regular polygon for all n>=3? If not, what is the
smallest n for which these three items are not sufficient?
