n=21: 439 reachable points of length <= 30, 102 classes of parallel directions
  class of alpha=0.139552: floating billiard finds 10 of the 10 (length, factor) pairs of the unfolding, none else
  class of alpha=0.284830: floating billiard finds 10 of the 10 (length, factor) pairs of the unfolding, none else
  class of alpha=0.165158: floating billiard finds 10 of the 10 (length, factor) pairs of the unfolding, none else
  class of alpha=0.474613: floating billiard finds 10 of the 10 (length, factor) pairs of the unfolding, none else
  class of alpha=0.246769: floating billiard finds 10 of the 10 (length, factor) pairs of the unfolding, none else
  class of alpha=0.826627: floating billiard finds 10 of the 10 (length, factor) pairs of the unfolding, none else
bands computed: 7676 (rays from O, both sides); largest number of segments of a simple preclosed piece: 78
odd n: in every class exactly m = 10 preclosed lengths c*lambda*sin(2j pi/n)/sin(pi/n), factors d_j = n'/gcd(n',j); classes by n': {21: 74, 7: 18, 3: 4, 1: 6}
  n'=21: factors 21,21,7,21,21,7,3,21,7,21  gcd 1  a quotient is n: yes  classes: 74
  n'=7: factors 7,7,7,7,7,7,1,7,7,7  gcd 1  a quotient is n: no  classes: 18
  n'=3: factors 3,3,1,3,3,1,3,3,1,3  gcd 1  a quotient is n: no  classes: 4
  n'=1: factors 1,1,1,1,1,1,1,1,1,1  gcd 1  a quotient is n: no  classes: 6
DONE n=21 [6.0s]
