question in solid state
 

[align=left]plz. in rotational symmetry we took that if a lattice remains unchange by a[align=left] rotation of 2(3.14)/n it said to have n_fold axis of symmetry, and n took numbers like 1,2,3,4,6,but didn't took 5,7... why? plz answering me as soon as u can. [/align] [/align]