For a positive integer , an angle of measure is trisectible if and only if does not divide .MacHale, Desmond. "Constructing integer angles", Mathematical Gazette 66, June 1982, 144–145. In contrast, is constructible if and only if is a power of or the product of a power of with the product of one or more distinct Fermat primes.
For a positive integer , an angle of measure is trisectible if and only if does not divide .MacHale, Desmond. "Constructing integer angles", Mathematical Gazette 66, June 1982 144–145. In contrast, is constructible if and only, if is a power of or the product of a power of with the product of one or more distinct Fermat primes.