21 into 13 best min fragment found: 21/4
  Cut up 21 sticks of length 13 like this:
    3 x (6 + 7)
    6 x (11/2 + 15/2)
    12 x (21/4 + 31/4)
  Reassemble as 13 sticks of length 21 like this:
    1 x (7 + 7 + 7)
    3 x (6 + 15/2 + 15/2)
    6 x (11/2 + 31/4 + 31/4)
    3 x (21/4 + 21/4 + 21/4 + 21/4)