To obtain these curves first look at 
torus knots
                with frequencies (2,3), (2,5) and (2,7). 		
        		Then twist one of the leafs to obtain more alternating crossings, implying
        		that the obtained curves are nontrivial knots. 
        		Such alternating knots cannot be drawn with fewer crossings.
        		
Morph_Prime_Knots_5_4_3.pdf